I know that nowadays you can get whatever kind of food you want in the UK or US but it still seems like both regions have a preference/iconic ethnic food that is popular. Even though Britain colonized India and imported foods from there they also dealt extensively in East Asia and didn't lose Hong Kong until the 20th century meanwhile the US had no Asian colonies but Chinese food is huge. What's up with that?
tl;dr: Immigrants.
Britain dealt a fair bit with China, but look at the context. Opium War, Arrow War, they were never even remotely as involved as they were in India. Even in China, the British police forces were Indian, plus you have the Gurkhas. The UK had Indian immigration earlier than they had Chinese immigration in much greater numbers, a few exceptions aside. Not to mention just how much earlier it was. Indians had been moving to England in large numbers in the early 1800s. It would be about 50 years before substantial East Asian immigration made it to the US. So while immigration into the UK was low, in general, compared to the US, Indian immigration was early and significant.
America meanwhile had Chinese immigrations, working as labourers mostly, from around the 1860s. The thing that they did way cheaper than whites in places like California was selling food. Japanese immigrants also were involved in cheap restaurants, and for both groups, rising nativist sentiment led to significant problems. Chinese food took off in the late 1800s because it was chap, it was good, and it was cheap. It was so cheap that non-Chinese staying in business in places like gold mining boom towns. Plus you've got things like the Boxer Indemnity Scholarship which brought students, although not large in number. The US also kinda had colonies in Asia, briefly, if you want to call them that (which I think we should, because, well, extraterritoriality), but aside from profiteers and missionaries, America mostly didn't care about China or America's potential interests in China. Meanwhile with the opportunities and focus on America and later Australia, Chinese simply weren't going to England in any large number. British Hong Kong was also pretty segregated.
It's all about immigrants establishing eateries, not colonies (though colonies can lead to immigrants). That's also why Asian American food is so weird; It's been heavily modified for American tastes from the very beginning.