Combine the beef, ¾ teaspoon salt and ¼ teaspoon black pepper.
Shape into 4 patties, ½-inch thick.
Grill the patties, 4 to 5 minutesper side or until the internal temperature reaches 160˚F.
Meanwhile, heat the olive oil in a large nonstick skillet over medium-highheat. A
Add the onions and cook for 2 minutes.
Stir in the mushrooms,barbecue sauce, remaining ¼ teaspoon salt and ⅛ teaspoon black pepper.
Cook and stir for 5 minutes or until tender. Place cheese slices over patties during the last minute of cooking. Serve the burgers in rolls topped with mushroom and onion mixture.