Pat the chicken breasts completely dry with paper towels to remove excess moisture. Using a sharp knife, carefully cut a deep horizontal pocket into the thickest side of each chicken breast, being sure not to slice all the way through. The pocket should be large enough to hold the filling but still leave a ½-inch border on the sides to prevent leakage. Once cut, season both sides of the chicken generously with salt, black pepper, paprika, and a light sprinkle of Italian seasoning. Gently rub the spices into the meat for even coating, then set the chicken aside on a plate while you prepare the filling.

In a large skillet over medium heat, melt one tablespoon of butter. Once the butter starts to bubble slightly, add three cloves of finely minced garlic. Sauté for about 30 seconds until the garlic becomes fragrant but not browned — this infuses the butter with that rich, garlicky aroma. Add one cup of finely chopped mushrooms to the pan and cook for 5–6 minutes, stirring occasionally, until the mushrooms release their moisture and start turning golden brown. If using baby spinach, add half a cup now and stir until just wilted, about 1–2 minutes. Remove the skillet from heat and allow the mixture to cool slightly before moving to the next step.

Transfer the sautéed mushroom and spinach mixture to a mixing bowl while still warm. Add half a cup of shredded mozzarella cheese and a quarter cup of shredded cheddar cheese. Stir until the cheeses start melting and create a creamy, cohesive filling. You can also add a pinch of salt or a dash of chili flakes here if you prefer a little heat. The mixture should be thick, scoopable, and evenly coated with melted cheese.

Spoon the cheesy mushroom filling evenly into the prepared chicken pockets. Use the back of the spoon to gently press the filling in so it sits snugly without overstuffing. If you notice the chicken is too full, remove a little of the mixture to prevent leakage while cooking. Secure the opening with toothpicks if necessary — this helps hold everything together during searing.

In the same skillet used for the mushrooms, heat another half tablespoon of butter or olive oil over medium heat. Once hot, carefully place the stuffed chicken breasts into the pan with the seam side up. Let them sear without moving for 4–5 minutes, allowing a golden crust to form. Flip carefully using tongs and sear the other side for another 4–5 minutes until equally golden brown. Spoon a bit of the hot garlic butter from the pan over the top as it cooks to lock in flavor and moisture.

Once both sides are beautifully seared, check the thickness of the chicken. If the breasts are thick, transfer the skillet directly to a preheated oven at 375°F (190°C) and bake for about 10 minutes until the internal temperature reaches 165°F (74°C). If your chicken is thinner, reduce the heat on the stove to low, cover the skillet, and cook for another 6–8 minutes until fully done.

Remove the chicken from the heat and let it rest on a plate for 5 minutes before slicing. This rest period allows the juices to redistribute inside the meat, keeping it tender and flavorful. Remove any toothpicks, drizzle with an extra spoonful of garlic butter from the pan, and serve warm. You’ll notice the creamy cheese and mushroom filling gently melting out with each slice — rich, garlicky, and absolutely irresistible.