Prepare oven: Preheat oven to 350°F.
Cook beef: Heat vegetable oil in a large skillet over medium-high. Add onion and cook until softened and translucent, about 6 minutes. Add garlic and cook for another minute. Add beef and break apart with a spoon; cook until brown. Add taco seasoning and stir to incorporate.
Add tomatoes and beans: Add black beans, pinto beans, tomatoes, green chiles, sour cream, ½ cup Cheddar cheese, and hot sauce, stir into meat mixture and allow to cook until the liquid thickens, about 5 minutes. Stir in frozen corn. Transfer mixture to a greased 9- x- 13-inch baking dish.
Add potatoes and bake: Line surface of casserole with a single layer of frozen Tater Tots. Cover dish with aluminum foil and bake for 30 minutes. Remove aluminum foil, sprinkle remaining ¼ cup Cheddar cheese over Tater Tots. Return to oven for 20 more minutes. Allow to cool slightly before serving.
