This has been asked before, but has often received poor shrift.

However, these , here, and especially /u/EvanRWT here and here address it

In short, India has a large diversity of cuisines, some spicy, others milder. Pepper, Long pepper, cubeb pepper, and variety of other spices were native to India and the Old World and could be used

cumin, ginger, pepper, coconut, coriander, asafetida (hing) and cardamom

/u/I_am_oneiros here has a writeup on Indian food pre columbian contact

The pepper trade with europe was important for a long time, and attested to during the roman era

Fun fact: In many cases,food offered at traditional temples can be rather similar to historical recipes.

“These temples, themselves, are sites of historical preservation,” says Gutiérrez. “You can step inside and experience food that tastes similar to how it would have tasted several hundreds of years ago.

Spice has always been an intrinsic part of most South Asian cuisines. Although India (using India here on to refer to the South Asian subcontinent in general) didn't always have chilli, we've had a lot of other spices -

Ginger (ārdraka/Zingiber Officinale) is considered native to South and South East Asia, and we get mentions of ginger in very early Sanskrit texts. Of course the more well-known 'traditional' source of spice in Indian food is pepper. Long pepper (pippali/Piper Longum) is indigenous to India and was once a major item of export, although now its use is much rarer. Black pepper was another major spice and continues to be used till date. Another spice was the *Chavya (*P. retrofactum), and it's been described as being 'weakly pungent with gingery overtones' (hardly ever used today outside of traditional medicine.) Other spices that weren't associated with the 'pungent' taste (heat/spice) but used to flavour food include cumin, garlic, asafoetida, methi, and the like- most of these are still used in Indian cooking.

New World Foods:

Six years after the Americas were discovered, Vasco da Gama discovered the sea route to India. This was a time of great exploration and bustling sea trade, and India was a major player in the world market. The Portuguese slave trade route, for example, was between South America to Africa, and the route extended to Goa (on the western coast of India) and other Portuguese settlements in SE Asia and China. The Spanish traded with the eastern coast of the subcontinent (Myanmar, Assam, and the Coromandel Coast). So new world foods really could enter the subcontinent multiple times, introduced in different regions by different people, and most Indians were already familiar with new world foods before British colonial rule.

Which foods are non-native to India but now used in Indian cuisine? Cashews were brought in from central Brazil very early on (we get a reference to cashews in India from 1578.) Papayas, tomatoes, and potatoes were all new world foods too- and chillies!

Chillies probably entered South India pretty early on and we know this because a Kannada song by the music composer Purandara Dasa (1480-1564) uses the chilli as a metaphor for human desire. Interestingly, he describes it as a 'saviour of the poor', so it was clearly accessible- and also already well-incorporated into Kannada cuisine. However, the Ain-i-Akbari (1590) that records the reign of the Mughal emperor Akbar does not have a single mention of the chilli, so the spread of the chilli to northern India was probably more gradual.

Most Indian cuisines went on to receive the chilli very well- from North East Indian cuisines, which use Bhut Jolokia/Ghost Chilli (the world's hottest chilli!), to North and West Indian cuisine, which not only extensively use chillies in food but also make a variety of chilli pickles, and then South Indian cuisine which uses them in chutneys and seasonings.

So what was food like before the chilli was introduced?

The Sangam texts of Tamil Nadu (6th C BCE - 3rd C CE) mention different ways of cooking animal meats: the thallittakari used meats that were first marinated with ground spices like pepper and mustard seeds and then fried in oil. Pulingari or Tuvai referred to meat that was boiled with pepper and tamarind, and could be ground and flavoured further to a paste (probably then eaten with rice).

From neighbouring Karnataka, we get the following description of a king's feast, dated around 1485 CE: "the women served an unfried brinjal baaji, which contained coconut shreds, curry leaves, and cardamom, mixed well, and flavoured with citrus juice and a little camphor... The tamarind side-dish and the pickle were consumed with great relish; the paapads were broken into pieces and the pacchadi eaten with delight. The meal was laid on broad banana leaves spread on the floor, and the kingly lords of the earth ate slowly until their appetites were satiated."

The Padmavat of the 16th century (Western India- Gujarat/Rajasthan) describes another feast, where the royal couple are fed 'wheat based rotis such as the lucchahi, poori, sohaari, and maanda, a liquid dhal dish, jhalar, many pickles (sandan), sugar syrup (kadohi), and sweet confectionaries like kandara (sweetened milk solids, today known as shakarapaka), kheer of jowar, and moranda.'

Most of these dishes and cooking styles still continue today, and interestingly don't compulsorily require the use of chillies (or other new world foods). Spicy pickles and chutneys were made with ginger and pepper (instead of chilli powder), south Indian rasams were made with tamarind instead of tomatoes. On the whole, there was no huge change in the nature of Indian cuisine- but since new world foods were used and substituted wherever possible, they brought new flavours and dishes, and left a very strong impact on the food of the subcontinent.

Source: Achaya, K. T. Indian Food: a Historical Companion. Oxford University Press, 2014.

Variants on this question come up here a fair bit, and as a result there's a response to it on our VFAQ. There's always more to say, but you might like to review it while you are waiting for fresh responses to your query:

What did "Old World" cuisines that are today known for their spicy foods taste like before chili peppers were imported from the Americas? - by /u/EvanRWT