Preheat oven to 375°F (190°C) and grease a casserole dish.
In a skillet cook ground beef and diced onion over medium heat until browned.
Drain excess grease and stir in taco seasoning and salsa.
Add black beans and corn and mix well.
Spread the beef mixture evenly into the prepared casserole dish.
Sprinkle cheddar and Monterey Jack cheese over the beef layer.
Arrange frozen tater tots evenly on top.
Bake for 30–35 minutes until the tater tots are golden and crispy.
Serve warm with optional toppings like sour cream, jalapeños, or chopped cilantro.