In a medium bowl, mix the chopped spinach, artichoke hearts, cream cheese, Parmesan cheese, mozzarella cheese, minced garlic, onion powder, Italian seasoning, salt, and pepper until well combined.
Pat the chicken breasts dry with a paper towel. Use a sharp knife to create a pocket in each chicken breast by cutting a slit horizontally through the center, being careful not to cut all the way through.
Generously fill each chicken pocket with the spinach and artichoke mixture, using toothpicks to secure the edges if necessary.
In a large oven-safe skillet, heat a drizzle of olive oil over medium-high heat. Season the outside of the stuffed chicken breasts with salt and pepper, then add them to the skillet. Sear for 4–5 minutes on each side, or until golden brown.
Transfer the skillet to the preheated oven and bake for 20–25 minutes, or until the chicken is cooked through (internal temperature reaches 165°F or 75°C).
Remove from the oven and let the chicken rest for a few minutes before slicing. This will help keep the juices in and make it more tender.
Notes
Serve on a bed of sautéed vegetables or a fresh garden salad. Drizzle with balsamic glaze for added flair.