Roast Peppers: (skip if using already roasted peppers) Heat a grill or grill pan to hot; or heat broiler. Cook peppers until completely charred, turning frequently so all sides cook evenly, 8 to 10 minutes. Remove from heat. Place peppers in a deep bowl, and cover bowl with plastic wrap. Set bowl aside until the skins loosen and the peppers are cool enough to handle. Using your hands, rub off the charred skin, rinsing your hands frequently under cold running water. Slice peppers in half, and remove the seeds and stems. Cut flesh into 1-inch-wide strips.
Make the vinaigrette: In a medium bowl, combine mustard and vinegar. Gradually whisk in olive oil. Whisk in 2 tablespoons warm water. Whisk in salt and pepper to taste, and set the vinaigrette aside.
Slice loaf of bread horizontally, and remove soft crumb; reserve crumb for another use. Spread olive paste on the bottom crust, and add the roasted red pepper strips. Crumble goat cheese on top of peppers. Arrange artichoke hearts over goat cheese. Drizzle half of the reserved vinaigrette on top. Arrange prosciutto and salami over artichoke hearts. Drizzle with the remaining vinaigrette. Scatter herbs over meats. Place the top crust on sandwich.
Wrap the sandwich tightly with plastic wrap. Set a weight, such as a brick or large cast-iron skillet on top for at least 1 hour. When ready to serve, slice sandwich into ten pieces.