1. Preheat oven to 400°F (200°C).

2. In a large oven-safe skillet over medium heat, melt butter. Add garlic and cook 1 minute until fragrant.

3. Add mushrooms, salt, pepper, and fresh parsley. Cook, stirring occasionally, until mushrooms are soft. Set mushrooms aside to cool (leave the pan juices in the skillet).

4. Pat chicken breasts dry. Season with salt, pepper, onion powder, and dried parsley.

5. Cut a pocket into each chicken breast by slicing a slit through the thickest side (don’t cut all the way through).

6. Stuff each breast with 2 slices mozzarella, then divide the mushroom mixture evenly among the 4 breasts. Top each with about 1 tablespoon Parmesan. Secure with toothpicks.

7. Reheat the same skillet with the pan juices over medium heat. Sear chicken until golden on both sides.

8. Cover skillet and transfer to the oven. Bake about 20 minutes, or until chicken is cooked through (165°F internal temp).

9. Serve with the pan juices and any extra mushrooms.

Optional Cream Sauce
10. Transfer chicken to a warm plate, keeping juices in the skillet. Add olive oil if needed, then sauté garlic 1 minute.
11. Lower heat. Stir in Dijon and half-and-half. Bring to a gentle simmer.
12. Stir in remaining mushrooms and Parmesan until melted. For a thicker sauce, whisk in cornstarch slurry.
13. Season with salt and pepper, add parsley, return chicken to the pan, and spoon sauce over the top to serve.