I always feel weird saying “Indian tacos” since they’re not at all Indian in the subcontinental sense and not really tacos in the Mexican sense. Also, I feel uncomfortable using “Indian” to refer to the First Nations of North America. But nobody says “First Nations tacos.” The Aboriginal friends I had growing up on the prairies in Canada would have laughed at me if I’d tried. Indian tacos are Indian tacos and they’re as authentically First Nations as Irish stew is Irish (despite the fact potatoes are native to South America) and as vindaloo is Indian (even though chilies too are from the New World).
What makes an Indian taco “Indian” is that, instead of a corn tortilla, it uses fried bannock, AKA fry bread. As to the rest, it usually contains meat, cheese, tomatoes, and lettuce. Sour cream is optional. Salsa is optional. If you want to make it even more North American Aboriginal, you can use ground bison. I, however, didn’t have any, so I used ground beef, which is, I would guess, the most common filling in Indian tacos anyway.