Heat grill pan or grill to medium-high heat. Brush eggplant, zucchini, and yellow squash with 2 Tbs. olive oil, and grill 3 to 4 minutes per side, or until charred and softened. Transfer to plate.Hollow inside of bread to make room for vegetables. Spread pesto on one side of bread. Spread tapenade on other side of bread.Layer eggplant, zucchini, yellow squash, roasted red peppers, and mozzarella on one side of bread. Drizzle with balsamic vinegar and remaining 1 Tbs. olive oil. Season with salt and pepper. Press top and bottom of sandwich together, and wrap tightly in plastic wrap. Place on baking sheet, and weigh down with heavy skillet or two large cans. Refrigerate 2 hours or overnight. Unwrap before slicing and serving.