Heat oven to 350 degrees. In a bowl, mix beef, onion, bread crumbs, seasoning, and egg. Press into an ungreased 2-quart glass baking dish. Or use these baking pan liners. It makes clean up a snap. Plus they are reusable.
After preparing the mashed potatoes, flavor with cheese. Then spread evenly over the meat mixture. Sprinkle more cheese, about a cup, over the top.
Bake about an hour, until the meat is cooked and reaches an internal temperature of 160 degrees. Sprinkle with chopped bacon, green onion, and tomatoes