Boy, where to begin....

For a start, the Spanish brought peaches, honeybees (most people don't realize those are an introduced species), and sheep and goats, all of which became bedrock cultural items for the Navajo and a few other Southwest tribes. To this day, Navajo and "mutton" or "wool" are all-but synonymous in certain trade circles, and I can tell you from experience that peaches and watermelons grown by Southwest tribes are ubiquitous and excellent. Bee-keeping doesn't appear to have endured much into the modern era.

Cows are another big one. Anybody else who lives in the intermountain west knows that cows basically rule the land, and most people with a bit of historical knowledge know that bison were exterminated to make room for them (to a point; it was also to cut off the Indigenous food/pelt supply). So, many tribal folks took to herding cows; it was that or abandon the land to find work in cities. Many of the grazing leases in the Four Corners are held by Utes, and a lot of Paiute families graze between there and California. With this came the adoption of beef steak, milk products, and so on.

The biggest part of this story, however, are the food items that were forced onto people. On early reservations and in literal concentration camps like Bosque Redondo, where the Navajo were forced to live for a while, growing or foraging for their traditional foods wasn't really possible. Instead they were given rations of white sugar, white flour, white lard, white milk, and so on. (Noticing a theme? That's no accident. Whiteness was associated with good health and purity, going back to European notions that compelled people to do things like powder their skin until they looked like porcelain dolls.) They adapted as best they could, and the longest-standing result is probably the most universal "Native American" food dish in most people's minds today: Indian fry-bread. This is why Indigenous-food traditionalists like Sean Sherman in his excellent book The Sioux Chef's Indigenous Kitchen basically despise the stuff.

That's a sample, anyway. For more related and interesting info, look up "Indigenous food sovereignty movement." I'm on RIF mobile to it's a real pain to try to type links into here long-hand but if people ask I can do so from my desktop later on.

Chief sources: I'm a doctoral candidate in archaeology with an emphasis in food and nutrition, so.... lots and lots of obscure articles. But check out Mann's 1492/1493 for good public scholarship on the topic, Burrillo's Behind the Bears Ears for info specific to the Four Corners, Sean Sherman's aforementioned book about Indigenous cooking, and if look into the food sovereignty movement you'll find loads of articles.