1. Arrange bacon on a paper towel-lined microwave-safe plate; cover with a paper towel. Microwave bacon at HIGH 2 minutes or until edges begin to crinkle and bacon is partially cooked.
2. Sauté mushrooms and onion in hot oil in a small nonstick skillet over medium heat 4 to 5 minutes or until tender and liquid is absorbed. Remove from heat, and stir in 2 Tbsp. barbecue sauce.
3. Preheat grill to 350° to 400° (medium-high). Shape ground beef into 8 (5-inch) thin patties. Place 2 Tbsp. mushroom mixture in center of each of 4 patties. Top with remaining patties, pressing edges to seal. Shape into 4-inch patties. Wrap sides of each patty with 2 bacon slices, overlapping ends of each slice. Secure bacon using wooden picks. Sprinkle patties with salt. Cover and chill 10 minutes.
4. Grill patties, covered with grill lid, over 350° to 400° (medium-high) heat 5 to 6 minutes on 1 side. Turn and baste with half of remaining barbecue sauce. Grill 5 to 6 minutes or until beef is no longer pink in center. Turn and baste with remaining barbecue sauce. Remove from grill, and let stand 5 minutes. Remove wooden picks. Serve burgers on buns, and top with remaining mushroom mixture.
Note: For testing purposes only, we used Kraft Honey Barbecue Sauce.