If using store-bought pizza dough, allow it to sit at room temperature for 30 to 45 minutes. Place the oven rack in the center position and preheat oven to 475 degrees Fahrenheit. Place a 12-inch cast-iron skillet in the oven to heat.
Lightly flour a work surface, the dough, and rolling pin. Roll 1 pound fresh pizza dough out into a 12-inch circle.
Carefully remove the skillet from the oven and place on a heat-safe surface. Add 1 tablespoon olive oil to the skillet and use a paper towel to spread into the pan evenly.
Carefully add the pizza dough to the skillet, spreading the edges into the corners of the pan. Lightly brush olive oil on the edges of the crust. Bake the pizza dough for 3 minutes to par-bake the crust.
Remove the pizza dough from the oven and evenly spread ½ cup pizza sauce over the dough. Sprinkle 1 cup shredded mozzarella cheese over the sauce. Add 16 small pepperoni slices, ½ cup thinly sliced bell pepper, ¼ cup thinly sliced red onions, ½ cup sliced white mushrooms, and ¼ cup sliced olives on top. Sprinkle ½ teaspoon Italian seasoning and black pepper.
Bake the pizza until the bottom is golden brown and crispy, 10 to 12 minutes. Slice the pizza and enjoy hot.