Prep the oven and pan: Preheat your oven to 400°F (200°C).
Lightly grease a baking dish or have an oven-safe skillet ready.
Soften the cream cheese: Let the cream cheese sit at room temperature for 15–20 minutes, or microwave it for 10–15 seconds to loosen it up.
Make the filling: In a bowl, mix cream cheese, mozzarella, Parmesan, garlic, spinach, green onions, herbs, lemon zest, lemon juice, a pinch of salt, black pepper, and red pepper flakes if using. Stir until smooth and well combined.
Prepare the chicken: Pat the chicken breasts dry. Using a sharp knife, slice a pocket into the side of each breast, keeping the opening small and being careful not to cut through the other side.
Season the chicken: Rub the outside of each breast with olive oil.
Sprinkle both sides with salt, black pepper, paprika, and onion powder.
Stuff the chicken: Spoon the cream cheese mixture evenly into each pocket. Don’t overfill—use what fits comfortably. Secure the opening with 2–3 toothpicks or tie gently with twine.
Optional sear: For extra color, heat a skillet over medium-high.
Sear the stuffed breasts for 1–2 minutes per side until lightly golden. Transfer to the baking dish if not using an oven-safe skillet.
Bake: Place the chicken in the oven and bake for 18–25 minutes, depending on thickness. The internal temperature should reach 165°F (74°C).
Rest and serve: Let the chicken rest for 5 minutes, then remove toothpicks.
Spoon any pan juices over the top. Serve with roasted vegetables, a side salad, or mashed potatoes.