In a large bowl, combine the pork, sausage, pepper, and salt. Form 4 patties, each about 3/4 inch thick. Place on a medium-hot grill and cook 6 to 7 minutes per side. (To cook on a stovetop, heat the olive oil in a grill pan over medium heat and cook the patties 8 minutes per side.) Serve on the onion rolls and top with ketchup and Sauteed Peppers and Onions, if desired.