Preheat oven to 400°F (200°C).

Using a sharp knife, carefully cut a pocket into each chicken breast. Season the inside and outside with salt and pepper.

In a large skillet, heat olive oil over medium-high heat. Add butter and melt. Sauté mushrooms for 5-7 minutes until golden, then add garlic and cook for 1-2 minutes. Remove from heat and cool slightly.

Combine mozzarella and Parmesan cheese in a bowl.

Fill each chicken pocket with the mushroom mixture and cheese mixture.

Place stuffed chicken in a baking dish. Bake for 25-30 minutes or until cooked through and cheese is melted.

Garnish with chopped parsley before serving.