Step 1: Prepare the Mushroom Filling

1. Heat a large skillet over medium heat and melt the butter.
2. Add the chopped mushrooms and cook for about 5 minutes until they release their moisture and start to brown.
3. Stir in the minced garlic, thyme, oregano, salt, and black pepper. Cook for another 2 minutes until fragrant.
4. Remove the skillet from the heat and let the mixture cool for a few minutes.
5. Stir in the shredded mozzarella, Parmesan cheese, and chopped parsley until well combined. Set aside.

Step 2: Prepare the Chicken Breasts

1. Preheat your oven to 375°F (190°C).
2. Using a sharp knife, cut a pocket into the side of each chicken breast, being careful not to slice all the way through.
3. Season both sides of the chicken with salt, black pepper, garlic powder, and onion powder.

Step 3: Stuff the Chicken

1. Carefully spoon the mushroom filling into each chicken breast pocket, pressing down gently to ensure it stays inside.
2. Use toothpicks to secure the openings if needed, preventing the filling from spilling out during cooking.

Step 4: Sear the Chicken

1. Heat a tablespoon of olive oil in a large oven-safe skillet over medium-high heat.
2. Sear the stuffed chicken breasts for 2-3 minutes per side until golden brown.

Step 5: Bake the Chicken

1. Transfer the skillet to the preheated oven and bake for 15-20 minutes until the chicken is fully cooked (internal temperature of 165°F or 75°C).
2. Remove from the oven and let the chicken rest for 5 minutes before serving.

Step 6: Serve and Enjoy

1. Garnish with fresh parsley and extra Parmesan cheese.
2. Serve hot with your favorite side dishes.