Preheat oven to 375-degrees.
Microwave potatoes, covered, for 5½ minutes in a microwave safe baking dish.
Toss potatoes with butter and Italian seasoning. Smash potatoes into a 7"circle in a 10" non-stick sauté pan. Sauté until golden brown on bottom, over medium heat, about 6-8 minutes. Flip browned potatoes onto a sheet pan and top with marinara sauce, mozzarella cheese and pepperoni.
Bake at 375-degrees until cheese is melted on top and is golden brown, about 12-15 minutes. Cut into 6 wedges and serve immediately.