Brown the ground beef along with the chopped onions and minced garlic in a large skillet over medium-high heat. Preheat the oven to 375 F.
Mix in the chopped green bell pepper, diced green chiles, taco sauce, and taco seasoning. Simmer until almost all the liquid has evaporated, about 8 minutes
Assemble the casserole: place half of the broken taco shells in the bottom of a 9x13-inch baking dish.
Add half of the meat mixture over the broken shells
Top the meat with half of the shredded cheese.
Repeat the layers ending with shredded cheese.
Bake until the cheese is bubbly, about 20 mins.
Top with your favorite toppings and serve while hot.