Preheat your oven to 375°F (190°C). Spray a 9x13 inch baking dish generously with cooking spray.

In a large, deep skillet or Dutch oven over medium-high heat, brown the ground beef, breaking it up as you go. Once the beef is fully cooked and no pink remains, drain off any excess grease.

Add the diced onion and cook until softened, about 5 minutes. Stir in the minced garlic and cook for 1 minute more, until fragrant.

Sprinkle in the chili powder, Worcestershire sauce, salt and black pepper. Stir well, letting the spices toast briefly.

Reduce the heat to low. Stir in the cream of mushroom soup, milk, and sour cream until the mixture is smooth and well combined.

Fold in the drained corn and the can of diced tomatoes with green chilies (undrained).

Pour the entire meat mixture evenly into the prepared 9x13 baking dish. Sprinkle half of the shredded cheddar cheese (about 3/4 cup) evenly over the top.

Carefully arrange a single layer of frozen tater tots over the cheese and meat mixture, close together.

Place the dish in the preheated oven and bake for 30 minutes, until the tater tots are firm and starting to crisp up around the edges.

Remove the casserole from the oven. Sprinkle the remaining 3/4 cup of cheddar cheese over the hot tater tots. Return to the oven and bake for another 5 to 10 minutes, or until the cheese is melted and bubbly, and the tater tots are golden brown and crispy.

Let the casserole rest on the counter for 5 to 10 minutes before slicing and serving.