Any ground meat works. Lamb, pork, or half sausage and half beef is fantastic. I used all lean beef but suggest you try 1 pound beef with 1/2 pound pork sausage.
I put a piece of parchment paper down just because I don't like foil touching acidic things while they bake.
If you don't use the sheet pan, your peppers are going to take less baking time.