Preheat oven to 375 F (190 C) and grease the bottom of a 9x13-inch baking dish.
In a large skillet over medium-high heat, cook ground beef until browned and completely cooked through, breaking it into small pieces as it cooks. Transfer beef to a bowl and set aside. Discard the remaining grease.
1 pound lean ground beef
In the same skillet, heat olive oil over medium heat, add onion and cook until soft, about 4 minutes. Add garlic and cook for 1 more minute.
1 tablespoon olive oil, 1 medium red onion, 2 clove garlic
Add cooked ground beef, taco seasoning, green chiles, and beans. Pour in 1/2 cup of water and bring to a simmer, stirring occasionally. Add 1-2 Tbsp more water if needed. Remove pan from heat.
¼ cup taco seasoning, ½ cup water, 1 can green chilies, 1 can black beans
Use 3 tortillas cut in half and 1 whole tortillas to line the baking dish (see picture above). Spread 1/3 of the salsa on top and then 1/2 of the meat mixture. Drop 1/2 of the sour cream over the meat and spread out with a spatula. Top with 1 cup of cheese. Repeat layers starting with flour tortillas. Then use remaining 4 tortillas, remaining salsa, and cheese.
12 flour tortillas, 24 ounces salsa, 1 cup sour cream, 3 cup shredded Mexican Cheese Blend
Bake for 30-40 minutes, or until the cheese is melted and lightly browned.