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 finely chopped yellow onion until beef is browned and onion is softened, approximately 6–8 minutes. Drain excess fat from the skillet.
03 - Sprinkle garlic powder, onion powder, kosher salt, and black pepper over the beef mixture. Stir thoroughly to distribute seasonings evenly.
04 - Pour condensed cream of mushroom soup and whole milk into the skillet. Stir until fully combined and smooth. Add frozen corn kernels and frozen peas (if using), mixing well.
05 - Transfer the beef and vegetable mixture into the prepared baking dish, spreading it into an even layer. Sprinkle shredded cheddar cheese evenly over the top.
06 - Arrange frozen tater tots in a single, uniform layer covering the entire surface of the casserole.
07 - Bake uncovered for 40–45 minutes 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 for easier scooping.