Preheat your oven to 375°F (190°C).
Slice each chicken breast horizontally to create a pocket.
Stuff each chicken breast with sautéed mushrooms, minced garlic, and shredded mozzarella. Secure with toothpicks.
Sprinkle Italian seasoning, salt, and pepper over each stuffed breast.
In a skillet over medium heat, melt olive oil and butter together. Sear the chicken on both sides until golden brown.
Transfer the seared chicken breasts to a baking dish and bake for 20–25 minutes, or until fully cooked through.
Once done, serve warm and enjoy!