What was Italian cuisine like before tomatoes were imported from the Americas?

The definitive primary source for anyone interested in this question is Bartolomeo Scappi's Opera dell'arte del cucinare (1570). It's after 1492, but tomatoes are not yet included in the cookbook, and will not be included in an Italian cookery book until Antonio Latini's Lo scalco alla moderna (1692), which includes a recipe for 'Salsa di pomodoro alla spagnola' (tomato sauce in the Spanish style).

Scappi was a cook for cardinals and popes, and thus his work is a better reflection of elite tastes than of what peasants ate. This incredible gastronomic tome has over a thousand recipes, quite well detailed with suggestions for alternate ways to produce a dish and advice or the best place or best season to find an ingredient. The best cheeses to Scappi, of course, were Parmesan.

Scappi is either one of the last great medieval cooks, or one of the first modern ones (and in reality, both). He treated his cooking as a neoclassical art form rather than a simple trade, but his dishes are essentially slightly more complex versions of what the nobility of Europe had been eating for centuries. His Opera includes many recipes for roasts, stews/soups, and pies- all stapes of medieval tables. Flavors often juxtaposed with each other more than complemented each other, and the preparation of elaborate, semi-edible displays of pastry and meat was very much still part of the spectacle of banqueting.

Roasted meats were seasoned with spices which have nowadays been all but relegated to desserts: cinnamon, cloves, nutmeg, mace, etc. The price, and therefore exclusivity, of these spices had made them into a way to demonstrate one's social standing during the medieval era. And of course, they do pair well with many meats, especially pork. Sugar, likewise, was used throughout meals instead of just during desserts, and features heavily in Scappi's recipes including in roasts and savory pies. This sweetness is a remnant of the cooking of ancient Rome, which had a predominance of sweet and sour flavors (honey and vinegar/juice).

Scappi's, as well as many other cookbooks of the period, included a section on dishes suitable for Lent or other fast days, dominated by recipes for fish, vegetables, and eggs. When the nobles made such abstemious dietary sacrifices, it is fair to say that they ended up with a diet closer to that of the lower classes, who could only afford grains, vegetables, and the occasional fish (if they lived on the coast) or a bit of offal.

But onto the part that everyone wants to hear about- what about pizza and pasta? Both existed in Italy before tomatoes, before even Marco Polo (allegedly and inaccurately) brought noodles back from China. Pasta in a recognizable form appeared in medieval Arabic cookbooks, and through the Arabs had been brought into Sicily. Scappi's noodles most often were cooked and served in broth or in thicker stews, much how rice was prepared. Scappi also had recipes for filled pastas (made without eggs) such as tortellini.

Pizza is a different story, as the word was used to describe something that few would consider pizza today. Scappi's most basic recipes for 'pizza' involve making a buttery pastry dough, and then baking it, brushing the top with beaten egg and at the end sprinkling it with sugar. It's a sweet pastry flatbread, served hot. One could also include rose water, cinnamon, or grated cheese.