For the spread: Combine the mayonnaise, roasted red peppers, lemon juice, pepperoncini and garlic in a small mixing bowl and whisk until combined. Season the spread with salt and pepper and set aside.
For the sandwich: Scoop out the center of each bread half, creating a hollow space for all the ingredients. Spread the herbed goat cheese on both sides of the bread and then add the roasted red pepper and pepperoncini spread. On the bottom half of the bread, lay the slices of prosciutto, salami and top with the artichokes. Top with the arugula, drizzle with balsamic vinegar and season with salt and pepper. Place the top half of the bread on top and wrap tightly in plastic wrap. Place the sandwich on a baking sheet and top with another baking sheet. Place a heavy pan (like cast iron) on the top baking sheet and store in the refrigerator, for at least 4 hours and up to overnight to allow the flavors to marry together. (If you can't fit 2 sheet trays in your refrigerator, just use the heaviest pan you have.)
To serve, unwrap the sandwich and slice into 8 to 10 individual servings.