In a large mixing bowl, mix together mozzarella cheese (save 2 tablespoons for later), and dry oregano. Set the cheese mixture aside.

Cook the Ground Beef and Vegetables:

Heat 1 tablespoon of olive oil in a skillet over medium heat. Add ground beef and cook until almost browned, breaking it up as it cooks. Add diced onions, bell peppers, and black olives, and cook for 1-2 more minutes until the vegetables soften. Remove from heat.

Add the cooked beef and vegetables to the cheese mixture in the mixing bowl. Gently mix in halved cherry tomatoes (if using) to complete the filling.

Roll out half of the pie crust dough on a floured surface to fit the bottom and sides of the 10-inch cast iron skillet. Press the crust into the skillet, letting some hang over the sides. Spoon the beef, cheese, and vegetable filling into the skillet, spreading it out evenly.

Lay half of the pepperoni slices over the filling. Roll out the second half of the pie crust and place it over the filling. Pinch the edges of the crusts together to seal. Cut a few small slits in the top crust to let steam escape. Brush the top with egg wash (1 egg beaten with 1 teaspoon of water) and sprinkle with oregano.

Arrange the rest of the pepperoni slices on the top crust, keeping them away from the slits. Sprinkle the saved 2 tablespoons of shredded mozzarella over the top.

Put the cast iron skillet on a baking sheet (to catch any drips) and bake in a preheated oven at 350°F (175°C) for 40-45 minutes, or until the crust is golden brown.

Take the skillet out of the oven and let it cool for 10 minutes before serving. Use a spatula to loosen the edges of the pot pie, then serve right from the skillet or transfer to plates. Enjoy the crispy crust and cheesy, gooey filling!