Set the oven to 400°F (200°C) to ensure it’s fully heated and ready to bake the chicken.

Using a sharp knife, carefully cut a pocket into each chicken breast, being cautious not to slice all the way through. Season both the inside and outside of the chicken breasts with salt and pepper to enhance the flavor.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add 1 tablespoon of butter and let it melt. Add the sliced mushrooms to the skillet. Cook, stirring occasionally, for about 5-7 minutes, or until the mushrooms are golden brown and tender. Stir in the minced garlic and cook for an additional 1-2 minutes until fragrant. Remove the skillet from the heat and let the mixture cool slightly.

In a small bowl, combine the shredded mozzarella cheese and grated Parmesan cheese. Mix well to evenly distribute the cheeses.

Fill each chicken breast pocket with an even portion of the mushroom mixture and cheese mixture. Be careful not to overfill to prevent spillage during baking.

Place the stuffed chicken breasts in a greased or parchment-lined baking dish. Bake in the preheated oven for 25-30 minutes, or until the chicken is fully cooked (internal temperature should reach 165°F/74°C) and the cheese is melted and bubbly.

Remove the chicken from the oven and let it rest for 5 minutes. Garnish with freshly chopped parsley for a burst of color and flavor. Serve hot with your favorite sides, such as roasted vegetables, mashed potatoes, or a crisp green salad.