Cut the Italian loaf in half horizontally and spread the Roasted Red Pepper Spread onto the cut side of both halves. On one half, evenly layer on the ham, then the mortadella, salami and provolone. Top with the romaine, radicchio and tomatoes, then top with the other half of the loaf. Cut into 1-inch sandwiches and serve with Quick-Pickled Zucchini on the side.
Roasted Red Pepper Spread:
Put the red peppers, mayonnaise, vinegar, oregano, red chile flakes and garlic in a food processor and pulse to combine well.
In a medium saucepan over medium-high heat, bring the vinegar, salt, mustard seeds, chile flakes and 3 cups water to a simmer. Cook until the salt has dissolved, about 5 minutes.
Divide the dill, garlic, zucchini and onions evenly between 2 quart-size mason jars.
Pour the hot liquid into the mason jars to cover the ingredients and let cool to room temperature, about 1 hour. Serve immediately or cover with lids and store in the refrigerator for up to a week.