Melt 3 tablespoons butter in an oven-safe skillet over medium-high heat, then add the finely diced cremini mushrooms. Cook 5-6 minutes until all moisture has evaporated, stirring occasionally so the mushrooms dry and turn lightly golden.

Add the minced garlic and fresh thyme leaves, then cook for 1 minute until fragrant. Stir constantly to prevent burning and keep the mixture aromatic.

Cool the mushroom mixture slightly so it doesn’t melt the cheese on contact. Let it rest briefly until warm rather than hot.

Stir in the shredded mozzarella cheese and grated Parmesan until evenly combined and glossy. Transfer to a bowl to use for stuffing once spreadable and thick.

Cut a deep pocket into each boneless skinless chicken breast. Slice carefully without cutting through so the pocket holds the filling.

Season the chicken inside the pockets and on the outside with salt, pepper, garlic powder, and smoked paprika. Apply generously so the flavor penetrates as it bakes.

Spoon the mushroom-cheese mixture into each pocket and press gently to pack it. Secure the opening with toothpicks so the filling stays contained during cooking.

Heat 2 tablespoons olive oil in the oven-safe skillet over medium-high heat. Sear the stuffed chicken 3-4 minutes per side until deeply golden with caramelized edges.

Transfer the skillet to a 400°F oven and bake for 18-22 minutes. Cook until the internal temperature reaches 165°F at the thickest part.

Remove the toothpicks from the chicken and drizzle with extra garlic butter. Let the garlic butter glisten on top for a rich finish.

Rest the chicken for 5 minutes before slicing. This helps the molten filling set slightly so it stays inside while still steaming when cut.