Cut bacon into 1” pieces. Cook bacon in 12” skillet until crisp, about 4-6 minutes. Crumble bacon and set aside. Pour bacon grease out of skillet, but don’t wash or wipe the skillet.
Cut chicken breasts so that no piece is more than 1” thick.
Add butter and olive oil to skillet. Saute chicken breasts in this mixture over medium heat, turning once, until chicken is almost cooked and just barely pink in center. The internal temperature should be 150 degrees F. This should take 8-10 minutes. Place chicken in ungreased 12x8” baking dish.
Cook onion and garlic in drippings remaining in skillet. Cook until onion is softened, then stir in salt, pepper, and cooked bacon.
Spoon over chicken breasts and sprinkle with cheese. Bake at 350 degrees for 10-15 minutes or until chicken is thoroughly cooked to 160 degrees F and cheese is melted.