In a large skillet, cook bacon over medium heat until crisp. Remove bacon and discard all but 2 tablespoons drippings. Saute onions in drippings until tender. Crumble bacon; add with mushrooms to skillet and set aside.

Meanwhile, combine beef, pork, cheese, pepper, garlic powder and steak sauce in a large bowl. Shape into 16 patties. Divide bacon mixture and place over eight of the patties. Place remaining patties on top and press edges tightly to seal.

Grill over medium heat until well-done (pork sausage in burgers requires thorough cooking). Serve on buns, with lettuce if desired.