Divide bread dough into 8 equal pieces. Place on a floured surface and cover dough with a towel. Let dough rest while preparing filling.
For filling, in a small covered saucepan cook onion and garlic in a small amount of boiling water until onion is tender. Drain. Stir in spinach and the 1 teaspoon Italian seasoning. In a bowl stir together egg, ricotta cheese, mozzarella cheese, and Parmesan cheese.
Roll each piece of dough into a 6-inch circle. Spread 2 tablespoons of the spinach mixture over half of each circle, spreading to within 1/2 inch of edge. Top with 1/4 cup of the cheese mixture. Moisten edges of dough with water. Fold each circle in half, pinching edges or pressing edges together with a fork. Prick tops with a fork. Lightly coat an extra large baking sheet with nonstick cooking spray; place calzones on sheet.
Bake in a 375 degree F oven for 20 to 25 minutes or until golden. Meanwhile, in a small saucepan stir together tomato sauce, the 1/2 teaspoon Italian seasoning, and the garlic salt. Heat through over medium heat. Serve with calzones. Makes 8 servings.