Preheat oven to 325 degrees F (165 degrees C). Grease a 2 quart casserole dish.
In a mixing bowl, combine mushroom soup, milk, cheddar cheese, and half of the onions. Mix together.
Layer the bottom of a 2 quart casserole dish with 1/2 of the green beans. Pour half of the soup mixture over beans, and add half of the processed cheese. Repeat layering, and top with remaining onions.