• Form ground sirloin into 6 equal-size patties and refrigerate.

  • Heat olive oil in a large nonstick skillet. Add onion and cook 5 minutes over medium

  • heat, stirring occasionally. Add pepper and mushrooms and cook an additional 4 to 5 minutes or until tender.

  • Heat gas grill to medium-high or coals in a charcoal grill to medium-hot. Lightly coat grill rack with oil or cooking spray

  • Grill burgers for 3 minutes per side, covered, or until internal temperature registers 160 degrees F on an instant-read thermometer. Turn off heat and place 2 slices of cheese on top of each burger. Cover and wait a few minutes until cheese melts.

  • Place burgers on Italian bread with onion and mushroom mixture spooned over top. Serve with pepperoncini, if desired.

Nutrition Facts

427 calories; 17 g total fat; 80 mg cholesterol; 648 mg sodium. 34 g carbohydrates; 36 g protein;