Preheat the oven to 375°F (190°C).

Heat 2 tablespoons olive oil in a small skillet over medium-high heat and brown the crumbled Italian sausage for 5 to 7 minutes until cooked through; drain on paper towels.

In the same skillet, sauté the diced bell pepper and onion with a pinch of salt for 4 to 5 minutes until softened; drain excess moisture.

In a large mixing bowl, combine the cooked sausage, pepperoni, ham, sautéed vegetables, shredded mozzarella, provolone, black olives, Italian seasoning, garlic powder, red pepper flakes, and salt and pepper; mix until cheese coats all ingredients.

Using a serrated knife, cut off the top quarter of the bread loaf and hollow out the interior, leaving a 1/2-inch shell; reserve the removed bread.

Spread 2 tablespoons marinara sauce inside the hollowed loaf evenly to coat the inner walls.

Stuff the filling mixture into the loaf, packing gently but leaving about 1/4 inch of space at the top to allow for cheese expansion.

Replace the bread lid, wrap the loaf loosely in foil leaving the top exposed, and place on a baking sheet.

Bake for 25 to 30 minutes until cheese is melted and the crust is golden; let rest for 3 to 5 minutes before slicing.