does he like black beans? Small red and black beans and rice make a GREAT taco filling. Just saute up an onion, red or green pepper, some garlic, add cumin, chili powder, coriander or whatever spices you do in your tacos, a pinch of brown sugar and some kind of tomato sauce. Add your beans simmer 10 minutes to meld flavors, add the rice or even quinoa or something (or you can leave it out and just do beans).
Whenever I make tacos I do two pans side by side, starting with the same ingredients in each and then adding my omni family ingredients in one, and beans in mine, though I still add beans to their too....