Preheat oven to 425℉
In a large bowl, combine the ricotta, mozzarella, spinach, artichoke hearts, garlic, salt, red pepper flake, and oregano. Mix well.
On a lightly floured surface, divide pizza dough into four equal parts. Spread or roll out the dough into rectangles about 1/8-inch to 1/4-inch thick.
Spoon an equal amount of cheese mixture onto one half of each dough piece, leaving about a 1/4-inch border. Fold the dough over to form the pocket then pinch around the border with your fingers or with a fork to firmly seal the edges.
Place each calzone on a baking sheet lined with parchment paper (or lightly sprayed with cooking spray.) Cut three slits into the top of each calzone.
Lightly brush the egg wash over the calzones. Be sure to get the edges of the dough as well.
Bake calzones for 20-25 minutes or until golden brown.
Allow calzones to cool for 5 minutes before eating (the filling will be very hot!) Serve with a side of marinara sauce.