Preheat oven to 375°F (190°C) and grease a 9x13 baking dish.
Cook ground beef in a skillet until browned.
Add onion and garlic; cook until softened. Drain excess fat.
Stir in taco seasoning and water; simmer 2–3 minutes.
Mix in salsa, black beans, and corn. Heat for 2–3 minutes.
Spread a layer of tortillas on the bottom of the baking dish.
Add a layer of meat mixture, then sprinkle cheese.
Repeat layers until ingredients are used, finishing with cheese on top.
Cover with foil and bake for 20 minutes.
Remove foil and bake another 10 minutes until bubbly and melted.
Let rest 5–10 minutes before serving.
Add toppings and serve warm.