Step 1Place a rack 3 inches from the heat source; turn on the broiler. Line a baking pan with foil. Cut off both ends of the peppers. Stand the peppers on a board and cut off the sides into 4 slabs. Arrange them on the prepared pan, skin side up. Broil until the skin is blackened, 5 minutes. Remove the peppers from the oven. Use the foil lining to wrap the peppers so they steam. Let them rest about 10 minutes, then slip off their skins. (The peppers can be refrigerated up to 3 days, or frozen up to 1 month. To freeze, put each pepper in small, airtight plastic bag.)
Step 2Trim the ends off the baguette. Rub a moistened paper towel over the crust to soften. Open the baguette and pull out the soft bread, leaving a 1/4-inch margin. Combine the mayonnaise, olive paste, vinegar and mustard in a small dish. Spread it evenly on the cut sides of the bread.
Step 3Cut the bell peppers, meats and cheese to fit the bread with no overhang. First, layer the red peppers in a single layer, then evenly layer the meats, cheese, tomatoes and basil leaves. Close the bread. Press gently with your hands. Cut the loaf in 3 equal portions. Wrap each airtight in plastic; twist the ends. Refrigerate 2 to 6 hours.
Step 4Unwrap the portions. Insert a toothpick into each, if needed, to keep the bread together. Cut each as desired (6 thin or 3 thick pieces). Remove the toothpicks. Arrange the sandwiches on a platter; garnish with basil sprigs.