Marinate the vegetables in the balsamic vinegar for at least an hour to overnight.
In a baking dish place the marinated veggies. Drizzle olive oil on top. Sprinkle salt and pepper. Bake at 450° for 10-20 minutes, or until tender. Cooking time will depend upon thickness of vegetables.
Roasted Garlic Mayo: slice about 1/2" off a head of garlic (the pointy end), exposing the cloves, and leaving the skin on. Put the garlic in aluminum foil and drizzle olive oil on top. Cover the garlic with the aluminum foil. Roast at 450° for 35-40 minutes, or until tender.
Squeeze garlic cloves out, mash with a fork, and mix in vegan mayo.
Spread garlic mayo on a slice of bread. Layer vegetables on the other slice. Sprinkle chopped basil on top. Top with the other slice of bread.