Preheat the oven to 350°F (175°C).
In a large skillet, brown the ground beef and chopped onion over medium heat until fully cooked.
Drain excess grease from the skillet.
Stir in the drained corn, green beans, cream of mushroom soup, milk, garlic powder, salt, and pepper into the skillet.
Transfer the mixture into a greased 9x13-inch baking dish.
Top with shredded cheddar cheese.
Bake the casserole in the preheated oven for 30-35 minutes, or until bubbly and the cheese is golden.
Let it cool for a few minutes before serving.
