In a small bowl, combine 1/2 cup Dijon mustard with 1/2 cup honey, 3 tablespoons mayo, and a squeeze of fresh lemon juice. Pour half the sauce into a small bowl, cover, and reserve for later.
Place the chicken in a large ziplock bag. Pour the remaining marinade into the bag and toss the chicken to coat. Chill in the refrigerator for at least two hours.
Preheat your oven to 400 degrees Fahrenheit.
In a small skillet, melt 1 tablespoon butter. Add the mushrooms and cook for 7-10 minutes, or until the mushrooms are tender and just starting to turn golden brown.
Heat a skillet or grill pan to medium-high heat. Remove the chicken from the marinade and season each piece with salt and black pepper. Place the chicken in the preheated pan. Cook for about 4 minutes, then when the chicken is golden brown, flip the chicken and cook for an additional 4 minutes. The goal here is to just sear the chicken and get a nice golden brown color on the outside. It will finish cooking in the oven later.
Transfer the chicken to an oven-safe casserole dish. Spoon some of the mushrooms on top of each piece of chicken. Break a piece of cooked bacon in half and arrange the bacon over the chicken. Divide the Monterey Jack cheese and the cheddar cheese evenly and sprinkle over each piece of chicken.
Place the chicken in the oven and bake for about 10 minutes (possibly longer if your chicken is really thick), or until the internal temperature of the chicken reaches 165 Fahrenheit and the cheese has melted.
Serve with remaining honey mustard sauce on the side. Sprinkle with chopped fresh parsley for garnish. Enjoy!