Heat a large skillet over medium-high heat. Cook and stir ground sausage in the hot skillet until browned and crumbly, 5 to 7 minutes; drain and discard grease.
Preheat oven to 350 degrees F (175 degrees C). Press 1 pie crust into the bottom of a 9-inch cake pan.
Combine sausage, marinara, green bell pepper, and onion in a bowl. Fill the bottom crust with marinara mixture and top with mozzarella cheese. Cover with the second crust, crimping the edges to seal. Cut an "x" in the top crust to release steam. Sprinkle Italian seasoning and garlic powder over top crust and arrange pepperoni over seasonings.
Bake in the preheated oven until crust is golden brown, 35 to 45 minutes.