1. Preheat the oven to 400°F 200°C and lightly coat a 9×13 inch baking dish with nonstick cooking spray.

2. Heat the olive oil in a large skillet over medium high heat. Add the lean ground beef, Italian sausage, and diced onion. Cook, breaking up the meat with a spatula, until the beef and sausage are browned and the onion is soft. Drain off any excess grease.

3. Stir in the minced garlic and cook for about 30 seconds until fragrant. Add the pizza sauce, Italian seasoning, crushed red pepper flakes if using, salt, and black pepper. Simmer for 3 to 5 minutes to thicken slightly and marry the flavors.

4. Unroll the refrigerated pizza dough and press it evenly into the bottom and slightly up the sides of the prepared baking dish, keeping the thickness as even as possible.

5. Par bake the crust for 7 to 8 minutes, just until it looks set but not browned, then remove the pan from the oven.

6. Spread half of the meaty pizza sauce over the par baked crust. Sprinkle with half of the shredded mozzarella and half of the grated Parmesan.

7. Repeat the layers with the remaining meat sauce, mozzarella, and Parmesan, making sure the top is well covered with cheese.

8. Arrange the pepperoni slices evenly over the top so each portion will have plenty of pepperoni.

9. Return the baking dish to the oven and bake for 18 to 22 minutes, or until the cheese is melted and bubbling, the pepperoni edges are crisp, and the crust is golden around the edges.

10. Let the bake rest for about 10 minutes to set, then sprinkle with chopped fresh parsley, slice into squares, and serve hot.