First, Sprinkle and rub the chicken breasts with seasoning salt. Cover and refrigerate for 30 minutes.
While the chicken is in the refrigerator, cook bacon in a large skillet until crisp. Remove bacon and set aside. ***Do not discard grease.***
Saute chicken in the bacon grease for 3 to 5 minutes per side, or until browned. Place chicken in a 9" × 13" casserole dish or pan.
To make the Honey Mustard: In a small bowl, mix the mustard, honey, mayonnaise and dried onion flakes.
Spread some of the Honey Mustard over each piece of chicken, then layer with mushrooms, crumbled bacon, and shredded cheese.
Bake in a 350° oven for 30 minutes, or until cheese is melted and chicken is done.
Serve with the left over Honey Mustard Sauce that you made.