Preheat your oven to 350° F.
Mix together the mustard, honey, mayonnaise, and Worcestershire sauce. Cover and refrigerate until ready to use.
Season your chicken breasts on both sides with salt and garlic powder. Set aside.
In a large skillet, cook the bacon until crisp over medium heat. Remove the bacon from the pan to a paper-towel lined plate. Remove all but 1 tablespoon of the bacon grease to a separate bowl.
Cook the chicken on both sides in the bacon grease until cooked through to 150-155° F, about 7-8 minutes total. Do this in 2 batches if needed.
Remove the chicken to a clean plate.
Add an additional tablespoon of bacon grease to the same pan and add the mushrooms, onions, and salt. Sauté for about 4-5 minutes until softened. Remove the mixture to a clean bowl and remove the pan from the heat.
Add the chicken to an oven proof baking dish and top with a spoonful of sauce on top followed by the mushrooms, bacon and then a sprinkle of both cheeses.
Bake for about 5-10 minutes just until the cheese is melted.
Remove from the oven and garnish with parsley and more sauce. Serve with your desired sides.