1. Preheat the oven to 350 F and spray a loaf bread pan with non stick cooking spray.
2. Add the flour, baking powder, salt, pepper, and baking soda to the bowl of a stand mixer and mix to combine. Slowly add the eggs and Olive oil, mixing until just combined. Add buttermilk, 1 1/4 cup of the mozzerella cheese, the 2 other cheeses, and the pepperoni and mix until just combined. Pour half the batter into the prepared bread pan, top evenly with the marinara sauce, then pour the remaining batter over the sauce. Top with the Italian seasoning and the remaining 1/4 cup mozzarella cheese.
3. Bake for 45 to 55 minutes or until a toothpick comes out clean from the center. Let cool for 15 minutes before removing from the pan. Slice the bread and serve with Giardiniera relish on the side.