Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with cooking spray or butter.

In a large skillet over medium-high heat, cook the ground beef and diced onion together, breaking up the meat with a wooden spoon as it cooks, about 7-8 minutes until the beef is no longer pink and the onions are translucent. Drain any excess fat.

Add the minced garlic, onion powder, chili powder, salt, and pepper to the skillet. Cook for 1 minute, stirring constantly, until fragrant.

Stir in the drained corn, cream of mushroom soup, milk, sour cream, and 1 cup of the shredded cheese. Mix over medium heat until the cheese begins to melt and the sauce becomes smooth and creamy, about 2-3 minutes.

Spread the beef and corn mixture evenly into the bottom of the prepared baking dish, smoothing it into an even layer that reaches all corners.

Arrange the frozen tater tots in a single, even layer over the beef mixture. Place them close together without overlapping.

Bake for 25-30 minutes, or until the tater tots are golden brown and crispy and the filling is bubbling around the edges.

Remove from oven and immediately sprinkle the remaining 1 cup of shredded cheese evenly over the hot tater tots. Return to the oven for 2-3 minutes until the cheese melts and becomes bubbly.

Let the casserole stand for 5 minutes before serving. Garnish with chopped green onions or cilantro if desired.