Preheat oven to 500 degrees.
Combine spinach, ricotta, mozzarella, oil, egg yolk, garlic powder, oregano, pepper flakes, and salt in a large bowl.
Place dough on lightly floured surface and divide into 4 even pieces.
With a rolling pin or your hands, flatten each piece into a 7 inch round on a piece of parchment paper.
Spread ¼ of spinach filling evenly over half of each dough round, making sure to leave a 1 inch border around the edge.
Brush the edges with the egg wash and then fold the other half of the dough circle over spinach mixture, leaving the bottom ½ inch border uncovered.
Press edges of dough together and pinch with fingers to seal.
With a sharp knife, cut 5 steam vents in top of calzones and brush tops with remaining egg wash.
Transfer calzones onto parchment lined baking sheet and bake for 8 minutes, brush with any remaining egg wash and sprinkle with grated parmesan, then bake for another 7 minutes.
Move to wire rack and let cool for 5 minutes before serving.
