Heat oven to 425°F. In large bowl, stir together sauce, 1 teaspoon of the Italian seasoning and the red pepper flakes. Stir in chicken, then stir in spinach. Spoon into skillet. Top with pie crust, turning under at edges inside skillet; flute. Cut slits in several places in top crust. Brush with melted butter; sprinkle with remaining 1 teaspoon Italian seasoning.