This is a BUNCO recipe. I've made it several times when I have to feed a crowd. To make it even better, look for homemade buns at a local bakery. I use homemade hamburger buns that are sold at the Maverick Gas Station. They are inexpensive ($2.19 for 8) and are surprisingly delicious.
Brown 1 lb. ground beef with chopped onions and chopped green peppers (desired amounts). Drain fat, then add 1 1/2 bricks (8 oz. each) cream cheese. Salt and pepper to taste. Add chopped, fresh button mushrooms and chopped, canned black olives. Continue cooking until mushrooms soften. Add 1 1/2 cups shredded mozzarella cheese just before serving. Serve on fresh buns.
Toasted Version: Don't add the mozzarella into the meat mixture. Split buns and spoon meat mixture onto bottom bun. Place a slice of mozzarella cheese on top. Place on cookie sheet and toast in oven at 400 degrees until cheese is melted and top bun is golden and toasted.