01 - Preheat oven to 400°F. Lightly grease a baking dish with cooking spray or oil.
02 - In a mixing bowl, combine spinach, artichoke hearts, cream cheese, mozzarella, Parmesan, garlic, and red pepper flakes. Mix until thoroughly blended.
03 - Pat chicken breasts dry with paper towels. Using a sharp knife, carefully cut a horizontal pocket into the thickest side of each breast, ensuring the knife does not pierce through to the other side.
04 - Season the outside of each chicken breast evenly with salt, pepper, and paprika.
05 - Divide the spinach-artichoke filling equally among the four chicken breasts, spooning the mixture into the pocket of each. Secure the openings with toothpicks to prevent filling from escaping.
06 - Heat olive oil in a large oven-safe skillet over medium-high heat until shimmering. Place stuffed 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, or move the seared chicken to the prepared baking dish. Bake for 20 to 25 minutes until the internal temperature reaches 165°F when measured at the thickest part.
08 - Remove chicken from oven and allow to rest for 5 minutes. Remove toothpicks carefully and transfer to serving plates.