Salt the pieces of eggplant, place on a wire rake, and let rest for 30 minutes. Preheat the oven to 400°F. In a bowl, combine the olive oil, balsamic vinegar, and pepper.
Prepare a baking sheet with nonstick spray. Pat the eggplant with a paper towel and transfer to the baking sheet. Brush both sides of the eggplant slices with the olive oil mixture. Roast the eggplant for 10 minutes. Flip and roast for another 10 minutes. Remove and set aside to cool slightly.
Combine all the ingredients for the sauce. Take the two slices of multigrain bread and smear each with a portion of the sauce.
On one of the slices, add the sliced avocado. Layer the meats on top of the avocado.
Add the roasted eggplant and the sliced tomatoes. Top with the romaine lettuce and the other multigrain slice.