Step 1: Prepare the Bread
Preheat your oven to 375°F (190°C). Line a large baking sheet with parchment paper. Using a serrated knife, slice the entire loaf of bread in half lengthwise, like you’re making a giant sub. Place both halves on the baking sheet, cut-side up.

Step 2: Create the Flavor Foundation
In a small bowl, combine the melted butter, minced garlic, Italian seasoning, dried oregano, red pepper flakes, and grated Parmesan cheese. Brush this garlic-herb butter mixture generously over the cut sides of both halves of bread. This will create the iconic, flavorful, crispy crust. Place the bread in the preheated oven for 5-7 minutes to toast lightly. This step prevents the bread from becoming soggy later.

Step 3: Build the Moisture Barrier
Remove the toasted bread from the oven. Spread the mayonnaise evenly over the bottom half of the bread. Then, drizzle the Italian dressing or sub sauce over the mayonnaise. This combination acts as a delicious barrier, protecting the bread from moisture released by the tomatoes and lettuce during baking.

Step 4: Layer the Meats and Cheeses
Now, begin layering the meats. Start with a layer of genoa salami, followed by the capicola (or ham), and finally the pepperoni. Layer them evenly, allowing some to ruffle and create height. Place the slices of provolone cheese over the entire layer of meat, creating a solid cheesy blanket that will melt and bind everything together.

Step 5: Add the Fresh Vegetables
Now, strategically add the vegetables. Scatter the shredded lettuce and thinly sliced red onion over the cheese. Arrange the tomato slices and pepperoncini peppers evenly across the top.

Step 6: “The Lock” and Final Butter Brush
Place the top half of the bread onto the loaded bottom half. Brush the top crust of the sandwich generously with the remaining garlic-herb butter. For an extra-crispy top, you can sprinkle a little more grated Parmesan over the buttered crust.

Step 7: Bake to Golden-Brown Perfection
Place the entire assembled sandwich back into the 375°F (190°C) oven. Bake for 12-18 minutes, or until the cheese is completely melted and bubbly and the top of the bread is a deep, golden brown and very crispy.

Step 8: Rest, Slice, and Serve
Carefully remove the baking sheet from the oven. It is crucial to let the sandwich rest for 3-5 minutes before slicing. This allows the molten cheese to set slightly, preventing a messy landslide of fillings when you cut it. Using a sharp serrated knife, slice the giant sandwich into 6-8 individual portions. Serve immediately while hot and gooey!