Prepare the Mustard Glaze: In a bowl, whisk together Dijon mustard, honey, mayonnaise, and lemon juice. Set aside.
Preheat the Blackstone Griddle: Set to medium heat and drizzle avocado oil over the surface.
Season and Cook the Chicken: Sprinkle salt and pepper on both sides of the chicken breasts. Place them on the hot griddle and cook for about 5-6 minutes per side.
Sauté the Mushrooms: While the chicken is cooking, push them to one side of the griddle and cook the mushrooms in the remaining avocado oil until tender.
Add the Mustard Glaze: Once the chicken is cooked through, brush the mustard glaze over the top.
Layer the Toppings: Evenly distribute the cooked mushrooms, chopped bacon, and shredded cheese over each chicken breast.
Melt the Cheese: Cover the chicken with a large griddle dome or tent with foil to help the cheese melt.
Garnish and Serve: Sprinkle with sliced green onions and serve hot.