01 - Preheat oven to 375°F. Lightly grease a 9x13 inch baking dish with cooking spray or butter.
02 - In a large skillet over medium heat, cook ground beef and chopped onion until beef is browned and onion is softened, about 6–8 minutes. Drain excess fat from the skillet.
03 - Sprinkle garlic powder, onion powder, salt, and black pepper over the beef mixture. Stir well to distribute the seasonings evenly.
04 - Pour condensed cream of mushroom soup and milk into the skillet. Stir until fully combined and smooth. Add frozen corn kernels and frozen peas if using, mixing to incorporate.
05 - Transfer the beef and vegetable mixture to the prepared baking dish, spreading it evenly across the bottom. Sprinkle shredded cheddar cheese over the top.
06 - Arrange frozen tater tots in a single, even layer covering the entire surface of the casserole.
07 - Bake uncovered for 40–45 minutes, or until tater tots are golden brown and crispy, and the filling is bubbling around the edges.
08 - Remove from oven and let the casserole rest for 5 minutes before serving to allow the layers to set.