Brown hamburger with the onions, then drain. Spray a 2 quart casserole dish with cooking spray. Mix the hamburger, milk and soups together. Spread on the bottom of the pan. Sprinkle with Cheddar cheese, then add a layer of green beans. Top with a layer of Tater Tots. Bake at 350 degrees for 45 minutes to 1 hour. 4 to 6 servings.