In a large bowl combine ground beef and sausage with your hands (it is not necessary to get it perfectly blended, it will mix further as patties are shaped). Shape meat mixture into 12 evenly sized balls. Pat each ball onto waxed paper to form a flat patty 4-1/2 inches in diameter. Place Parmesan pieces and chopped red sweet peppers on top of 6 of the patties. Top with remaining meat patties to make 6 burgers. Press gently to seal edges. Season with salt and pepper.
For a charcoal grill, arrange medium-hot coals around a drip pan. Test for medium heat above the pan. Place patties on grill rack over drip pan. Cover and grill for 18 to 22 minutes or until an instant-read thermometer inserted slightly away from the center of the burger registers 160 degree F. (For gas grill, preheat grill. Reduce heat to medium. Adjust for indirect cooking. Grill as above.) If desired, brown the top of the patties by moving the burgers directly over the coals for the last 2 to 3 minutes of cooking.
To serve, place each burger between lettuce leaves on individual plates. Use toothpicks to attach a cherry tomato to each. Makes 6 servings.