Make the filling: In a skillet, melt 1 tbsp butter over medium heat. Add mushrooms and cook until softened (about 5 minutes). Add garlic, thyme, and parsley, cooking 1–2 more minutes. Remove from heat and mix with cream cheese and mozzarella until well combined.
Prep the chicken: Slice a pocket into the side of each chicken breast, being careful not to cut all the way through. Stuff each with the cheesy mushroom mixture and secure with toothpicks.
Sear the chicken: In an oven-safe skillet, melt remaining 2 tbsp butter over medium-high heat. Sear chicken breasts 2–3 minutes per side until golden brown.
Bake: Transfer skillet to oven and bake for 20–25 minutes, or until chicken is fully cooked (internal temp should hit 165°F/74°C).
Serve & impress: Spoon some of the melted garlic butter over the top, garnish with a sprinkle of parsley, and serve hot with veggies or pasta.
