1. Heat oven to 375 degrees. Spray a square baking dish, 8x8x2-inches, with nonstick cooking spray.
2. Rinse chicken and pat dry.
3. In medium bowl, combine all ingredients except the chicken and marinara sauce. Using fingers, carefully stuff about 1/3 cup of spinach mixture under the skin of the chicken. Secure skin with toothpicks.
4. Place stuffed breasts, skin side up, in baking dish. Bake 25 to 30 minutes or until chicken is golden brown and no longer pink when cut into.