Preheat oven to 350 degrees Fahrenheit.
In a small bowl or dish, combine the onion powder, garlic powder, paprika, dill, parsley, salt, and pepper.
Next, in a bowl, combine the Gruyere cheese, cream cheese, parmesan cheese, and mozzarella cheese.
Heat a small pan to medium. Add a teaspoon of the oil. Add the chopped bacon. Cook until the bacon just begins to crisp up. Transfer the bacon to the cheese mixture.
In the same pan you cooked the bacon, add the butter, followed by the mushrooms. Lower the heat to low-medium. Cook the mushrooms until they begin to cook down in size. Transfer the mushrooms to the cheese mixture.
Using a sharp knife or kitchen scissors, cut a pocket on the side of each chicken breast. Make the pocket large enough to stuff a generous amount of the filling in the chicken. Sprinkle a little bit of salt on the inside of the pocket.
Rub the outside of the chicken with some oil and then with the prepared spice rub.
Stuff the inside of the chicken with your prepared filling. Your stuffing should be facing up so that it doesn't spill out when cooking.
Bake in the preheated oven for about 50 to 55 minutes, or until the chicken registers 165 degrees Fahrenheit internally. The baking time will vary slightly, depending on the size of the chicken breasts you use.