Preheat your oven to 350°F.

In a large skillet over medium heat, cook the ground beef and onion, breaking the beef apart with a spoon, for about 5-6 minutes until the beef is browned and the onions are tender. Drain any excess fat.

Stir in the taco seasoning and water, then add the black beans. Let the mixture simmer for a few minutes until it thickens slightly.

In a separate bowl, combine the diced tomatoes with green chiles and sour cream to create the sauce.

Lightly grease an 8-inch square baking dish. Place one flour tortilla at the bottom of the dish.

Layer half of the beef and bean mixture over the tortilla, followed by half of the tomato and sour cream sauce, and sprinkle with one-third of the cheese.

Repeat the layers with the remaining ingredients, finishing with a tortilla and the remaining cheese on top.

Cover the dish with aluminum foil and bake in the preheated oven for 30-40 minutes, or until the casserole is heated through and the cheese is melted.

Remove the casserole from the oven and let it sit for a few minutes before slicing. Serve with your favorite burrito toppings, such as sliced avocado, chopped cilantro, or a dollop of guacamole.