01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish.
02 - Rub chicken breasts with olive oil, salt, and black pepper. Arrange in single layer in prepared baking dish.
03 - In large bowl, combine spinach, artichoke hearts, cream cheese, sour cream, mayonnaise, garlic, mozzarella, Parmesan, onion powder, and red pepper flakes. Mix until smooth and well combined.
04 - Evenly spread spinach-artichoke mixture over chicken breasts.
05 - Sprinkle topping mozzarella and Parmesan evenly over casserole.
06 - Bake uncovered for 25 to 30 minutes until chicken is cooked through to internal temperature of 165°F and top is golden and bubbly.
07 - Let rest for 5 minutes before serving. Serve with side salad or steamed vegetables if desired.