1. **Preheat Oven:**

– Preheat your oven to 200°C (400°F).

 

2. **Prepare the Mushroom Filling:**

– In a large oven-proof skillet, melt butter over medium heat.

– Add minced garlic and sauté until fragrant (about 1 minute).

– Add sliced mushrooms, season with salt and pepper, and cook until soft.

– Stir in chopped parsley and set aside to cool.

 

3. **Prepare the Chicken:**

– Pat the chicken breasts dry with paper towels.

– Season each breast with salt, pepper, onion powder, and dried parsley.

– Using a sharp knife, cut a pocket into the thickest part of each breast.

 

4. **Stuff the Chicken:**

– Place a slice of mozzarella cheese into each chicken pocket.

– Fill each pocket with the mushroom mixture.

– Top the mushroom filling with a tablespoon of grated Parmesan cheese.

– Secure the openings with toothpicks.

 

5. **Sear the Chicken:**

– In the same skillet, heat olive oil over medium heat.

– Add the stuffed chicken breasts and sear until golden on both sides.

 

6. **Bake the Chicken:**

– Transfer the skillet to the preheated oven.

– Bake for 20 minutes, or until the chicken is cooked through and no longer pink in the center.

 

7. **Prepare the Garlic Parmesan Sauce (Optional):**

– In the same skillet, heat olive oil over medium heat.

– Add minced garlic and sauté until fragrant.

– Stir in Dijon mustard and half and half, bringing the mixture to a gentle simmer.

– Add grated Parmesan cheese, stirring until the sauce thickens.

– Season with salt and pepper to taste.

– If desired, add the cornstarch slurry to thicken the sauce further.

– Stir in chopped parsley.

 

8. **Serve:**

– Remove toothpicks from the chicken breasts.

– Serve hot, drizzled with the garlic Parmesan sauce if using.