Grill the red peppers over medium heat until charred. Place in a paper bag and steam for 10 minutes. Scrape off skins from peppers. Cut in half, remove the stems and seeds and set aside. Brush the mushrooms, eggplant, zucchini, and onions with sesame oil. Season with salt and pepper. Grill the vegetables on medium heat, turning twice; approximately 8 minutes for the mushrooms, 6 minutes for the eggplant, 3 minutes for the zucchini, and 4 minutes for the onion. Remove from the heat and place on a plate. Brush and grill garlic - watch carefully so it does not burn - remove promptly. Sprinkle with thyme.
Place 2 halves of the red pepper, balsamic vinegar, and grilled garlic in a blender. Add the olive oil and season with salt and pepper. Puree until smooth.
Brush the bread slices with olive oil and grill on medium heat for 1 minute on each side. Divide the vegetables evenly on 8 slices of bread. Top with the red pepper sauce and sprinkle with basil. Stack a bread slice with vegetables on each of 4 slices with vegetables, and top these 4 sandwiches with the 4 remaining bread slices. Secure with toothpicks and slice in half. Serve with the leftover red pepper sauce.