Cook diced cremini mushrooms in butter over medium-high heat for 5-6 minutes until all moisture has evaporated, stirring so they dry out and start to caramelize. You should see the pan steam fade and the mushrooms look reduced and glossy, not wet.

Add minced garlic and fresh thyme leaves, then cook for 1 minute until fragrant. The aroma should turn sharp and fragrant within about 60 seconds.

Cool the mushroom mixture slightly for 2-3 minutes so the dairy won’t seize when added. Let it rest just until it’s warm, not hot.

Stir in shredded mozzarella cheese and grated Parmesan cheese until melted and cohesive. The filling should look thick and creamy with cheese strands visible as you stir.

Cut a deep pocket in each boneless skinless chicken breast, keeping the bottom intact. The opening should be large enough to spoon in filling.

Season inside the pockets and the outside of the chicken breasts generously with salt, pepper, garlic powder, and smoked paprika. The surface should look speckled and evenly dusted.

Fill each pocket with the mushroom cheese mixture and secure the opening with toothpicks. The filling should sit just below the surface without overflowing.

Heat olive oil in an oven-safe skillet over medium-high heat and sear the stuffed chicken for 3-4 minutes per side until golden. Use visual cues: deep brown color and a crisp sear ring around the chicken.

Bake at 400°F for 18-22 minutes until the internal temperature reaches 165°F. The chicken should look set and the juices should run clear when pierced.

Remove toothpicks, drizzle with extra garlic butter, and rest 5 minutes before slicing. The resting period helps the molten filling thicken slightly so it won’t flood out instantly.