1) Preheat oven to 350 degree.
2) Cut a thin slice from the top of the pepper, scoop out seeds and membrane and boil in salted water for 10 minutes.
3) Drain and keep aside.
4) Shape ground beef into patty, brown in butter and break into small chunks.
5) Stir pork and beans, onion, catsup, mustard and spoon into the pepper cups.
6) In a baking pan, place the pepper cups and bake for 20 minutes.
7) Garnish with the remaining onions and bake for 10 minutes further until onions are crispy.