In a large bowl combine egg, chopped onion, panko, 2 tablespoons peach preserves, Worcestershire sauce, oregano, and black pepper. Add ground beef and ground pork and mix well. Shape mixture into four 3/4-inch thick patties.
For a charcoal or gas grill, grill patties on the rack of a covered grill directly over medium heat for 14 to 18 minutes or until done (165 degrees F), turning once and spreading with remaining 2 tablespoons peach preserves halfway through grilling. If desired, top with onion slices and cheese and grill 1 minute more or until melted.
Serve patties on buns with barbecue sauce, if desired.