Preheat oven to 450 degrees F. Line baking sheet with parchment paper. Set aside.
Heat olive oil in skillet over medium heat. Add sausage and cook until heated. Remove sausage and set aside. Add spinach to skillet. Cook until just wilted, about 1 minute. Remove and place in another bowl. Set side.
Divide pizza dough into four equal parts. On a lightly floured surface, roll dough to a circle about 7-inches in diameter. Spoon about 1 1/2 tablespoons of sauce onto half of dough. Top with sausage, tomatoes, and spinach. Season with salt and red pepper flakes, if desired. Sprinkle mozzarella cheese. Fold plain half of dough up over filling. Pinch edges together to seal. Place on prepared baking sheet.
Sprinkle grated parmesan cheese and shredded mozzarella cheese over calzones. Bake for 18-20 minutes until dough is brown and cheese has melted. Serve warm with additional sauce for dipping.