Combine 1 1/2 cups flour, yeast and salt in large mixing bowl. Add water and 2 Tbps. oil. Beat with an electric mixer on low speed 30 seconds or until combined. Beat on high speed 3 minutes. Stir in as much of the remaining flour as possible.
Turn dough onto lightly floured surface. Knead in enough remaining flour until dough is smooth and elastic, about 7 minutes. Place dough in lightly oiled bowl and turn to oil top. Cover and let rise in warm place until doubled in size, about 40 to 50 minutes.
Make the Filling
Heat 1 Tbsp. oil in a large skillet over medium heat. Add onion and garlic. Cook, stirring occasionally, 4 minutes, or until onion is tender. Add mushrooms and cook 2 minutes, or until mushrooms are tender. Add spinach and cook 2 minutes until spinach is wilted.
Remove from heat and stir in mozzarella and Parmesan cheeses.
Prepare the Calzone
Preheat oven to 400°F.
Turn dough onto lightly floured surface. Punch down to remove air bubbles. Divide dough into fourths and let rest 10 minutes. Pat or roll dough into four 6-inch circles.
Spread 2 Tbsp. pizza sauce on half of each dough circle leaving a 1-inch border. Top evenly with spinach filling. Moisten edges of dough with water. Fold dough over filling to make four half-moons. Seal edges by pressing with tines of a fork. Prick tops.
Place on greased baking sheet. Bake 20 minutes, or until golden brown.
Let stand 5 minutes. Serve with remaining pizza sauce that has been heated.