Preheat oven to 375°F and lightly grease a 9x13-inch baking dish with cooking spray.
Heat olive oil in a large skillet over medium-high heat, add onion and garlic, and cook for 2 minutes until softened.
Add ground beef to skillet and cook until browned, breaking it apart as it cooks, then drain any excess fat.
Stir taco seasoning, diced tomatoes with green chiles, and 1/2 cup water into the beef, simmer for 5 minutes until thickened.
In a bowl, combine black beans, corn, and 1 cup of salsa.
Spread 1/2 cup salsa on the bottom of the prepared baking dish, then layer 4 tortillas to cover the bottom (overlapping as needed).
Spread half of the beef mixture over tortillas, followed by half of the bean mixture, 1 cup cheese, and dollops of 1/3 cup sour cream.
Repeat layers with 4 more tortillas, remaining beef, remaining bean mixture, 1 cup cheese, and 1/3 cup sour cream.
Top with final 4 tortillas, remaining salsa, and remaining cheese.
Cover with foil and bake for 30 minutes, then remove foil and bake 10 more minutes until cheese is melted and edges are golden.
Let stand for 10 minutes before cutting, then serve with desired toppings.