Preheat oven to 375°F. Spray 9x13-inch baking dish with non-stick spray.
Brown ground beef and onion in large skillet over medium-high heat, 7-8 minutes.
Drain excess fat, leaving about 1 tablespoon.
Add taco seasoning and water. Simmer 2-3 minutes until absorbed.
Stir in black beans, corn, salsa, green chiles, garlic powder, and cumin. Cook 2-3 minutes.
Remove from heat. Stir in sour cream and 1 cup cheddar cheese.
Spread beef mixture evenly in prepared baking dish.
Sprinkle Monterey Jack and ½ cup cheddar over beef layer.
Arrange frozen tater tots in single layer on top.
Bake 40-45 minutes until tots are golden brown and crispy.
Sprinkle remaining ½ cup cheddar over tots. Bake 3-5 minutes until melted.
Let rest 10 minutes before serving. Top with favorite taco toppings.