Cast-Iron Skillet Calzone

I'll be preparing this delightful spin on the traditional Italian dish for supper tonight. The family always loves it and more often than not, I end up making two just so we have enough for leftovers. I urge you to customize it to your liking and experiment with new ingredients. If you prepare it for you and yours, and/or put your own spin on it, please let me know in the comments.

Preparation time: 30 minutes
Baking time: 25 minutes
Baking temperature: 400°F
Standing time: 5 minutes

Required ingredients:
1/2 lb. ground sirloin or ground turkey
1/2 lb. Italian sausage with casings removed (mild or hot, your choice)
6oz. Sliced pepperoni
1/4 cup chopped sweet onion
1 lb. fresh (or frozen) pizza dough, thawed
1 cup marinara sauce
2 cups shredded mozzarella cheese or Italian cheese blend (8oz.)
1 cup sliced fresh baby bella mushrooms
1 cup chopped red and/or yellow sweet peppers (2 small)
1/2 tsp. dried oregano, crushed
1/4 to 1/2 tsp. crushed red pepper

Optional ingredients:
Grated Parmesan cheese
Snipped fresh flat-leaf Italian parsley
Extra warmed marinara sauce (for dipping) 

Steps: 
1) Preheat oven to 400°F. In a 9.5 to 10-inch cast-iron or other heavy oven-going skillet cook beef, sausage, and onion over medium-high heat until meat is browned and onion is tender, using a wooden spoon to break up meat as it cooks. Drain meat mixture in a colander/strainer). Wipe out skillet with a paper towel; cool slightly.
2) On a lightly floured surface, divide pizza dough in half. Roll one dough portion into a 12-inch circle (if dough is hard to roll, let stand for 5 minutes and then roll out). Press dough circle onto the bottom and up the sides of the skillet. Spread 1/2 cup of the marinara sauce over dough in skillet. Top with meat mixture, sliced pepperoni, mozzarella/Italian shredded cheese, mushrooms, sweet peppers, oregano, and crushed red pepper. Drizzle remaining 1/2 cup of marinara sauce over filling. Roll the remaining dough portion into an 11-inch circle. Place dough circle on top of filling. Pinch edges of bottom and top crusts together to seal. Using a sharp knife, cut slits in top crust.
3) Place skillet in oven. Bake about 25 minutes or until crust is golden brown and filling is bubbly. Let stand for 5 minutes before serving. Optionally, sprinkle with Parmesan cheese and/or parsley. Cut into six wedges. Serve with additional, optional warmed marinara sauce.