01 - Preheat oven to 400°F. Lightly grease a baking dish and set aside.
02 - In a mixing bowl, combine spinach, artichoke hearts, cream cheese, mozzarella, Parmesan, garlic, and red pepper flakes. Mix until well incorporated.
03 - Pat chicken breasts dry with paper towels. Using a sharp knife, carefully cut a horizontal pocket into the thickest side of each breast, being careful not to cut completely through.
04 - Season the outside of each chicken breast evenly with salt, pepper, and paprika.
05 - Divide the spinach-artichoke mixture evenly among the four chicken breasts, filling each pocket generously. Secure the openings with toothpicks.
06 - Heat olive oil in a large oven-safe skillet over medium-high heat. Once hot, place chicken breasts in the skillet and sear for 2 to 3 minutes per side until golden brown.
07 - Transfer the skillet to the preheated oven and bake for 20 to 25 minutes until the internal temperature of the chicken reaches 165°F at the thickest part.
08 - Remove from oven and allow chicken to rest for 5 minutes. Remove toothpicks and transfer to serving plates.