1Chop chicken breast and season with garlic powder, kosher salt, pepper, cumin, and chili powder.
2Heat olive oil in a skillet, then cook chicken in a single layer until browned.
3Add onion and cook while stirring.
4Add pinto beans, green enchilada sauce or tomatillo salsa, and diced green chiles; simmer until the sauce thickens, smashing some beans with a fork to help thicken.
5Butter a casserole dish and one side of each flour tortilla.
6Build tacos in the dish by placing a buttered tortilla down, adding a little cheese, filling, and more cheese; fold the tortilla and nestle it against the edge of the dish, repeating with remaining tortillas.
7Top with remaining shredded monterey jack cheese and bake in a preheated oven.
8Make a topping sauce by mixing sour cream with a portion of the green enchilada sauce or tomatillo salsa.
9Top finished tacos with shredded lettuce and the sour cream sauce before serving.