**Preheat Oven:** Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or foil for easy cleanup.
**Prepare Bread:** Brush the cut sides of the bread with olive oil. Sprinkle evenly with Italian seasoning and garlic powder.
**Assemble Sandwich:** On the bottom half of the bread, layer the provolone cheese, salami, pepperoni, and mortadella. Top with roasted red peppers, banana peppers, and spinach leaves. Drizzle with balsamic glaze if using. Place the top half of the bread on the sandwich.
**Toast in Oven:** Place the assembled sandwich on the prepared baking sheet. Bake for 8-10 minutes, or until the bread is golden and the cheese is melted.
**Slice and Serve:** Remove the sandwich from the oven, let it cool slightly, and slice into individual portions. Serve warm.