Preheat oven to 400ºF.
In a large skillet over medium heat, add oil and when hot, add onions, red peppers and mushrooms. Season with freshly ground black pepper and sauté the vegetables until tender, about 5 minutes.
Add garlic and sauté for 1 minute. Add sausages and cook for 5 minutes.
Transfer the meat mixture to a medium bowl. Stir in Italian seasoning, oregano, basil, red pepper flakes, parsley, and pizza sauce; set aside.
Place dough on a floured work surface, pull under to form a ball; divide it into 4 equal pieces. Pull under to form 4 balls and then roll it down to a round shape of about 9-inch diameter.
Spread the meat mixture over half of the dough, leaving at least 1” from the edge. Top with cheese over the meat mixture.
Moisten the edge of the dough with water using damp fingers and fold over the top just past the filling, tap it down to keep it in place. Take the extra dough and fold it over, going around, crimping it to seal the edge.
Sprinkle cornmeal on a baking sheet lined with a silicone mat.
Using a bench scraper, carefully transfer the calzone to the prepared baking sheet. Make a couple air vents with the tip of a knife. Brush an egg wash over and sprinkle lightly with parmesan cheese.
Transfer to the preheated oven and bake for 15-20 minutes or until golden.
Remove from the heat and let them rest 10 minutes before slicing. Cut in half and serve with a side of Marinara Sauce and salad.