Preheat oven to 400°F (200°C) and grease a 9x13 baking dish.
In a skillet, cook ground beef 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, beans, and corn; cook for 2–3 minutes.
Spread meat mixture evenly in baking dish.
Sprinkle 1 cup cheddar and ½ cup Monterey Jack cheese over meat.
Arrange frozen tater tots in a single layer on top.
Bake for 35–40 minutes until tots are golden and crispy.
Remove from oven, add remaining cheese, and bake 5 more minutes until melted.
Rest 5 minutes before serving.
Add toppings and serve warm.