This vegetarian sandwich is full of flavor — marinated eggplant, grilled to perfection, is piled high on top of layers of fresh tomato, red onion, and spinach and results in a satisfying meal that won't leave you feeling stuffed.
In 1 large or 2 medium-sized flat dishes, combine the tamari, water, paprika, garlic powder, onion powder, and cayenne, if using, and stir. Place the eggplant in the dish to marinate for at least 20 minutes.
Preheat a gas grill on medium heat.
Place the eggplant on the grill and cook for 5-7 minutes on 1 side and flip and cook the other side for 5-7 minutes. Remove from the heat and set aside.
Turn the oven to broil. Place the bread on a baking sheet and spread mustard on the bread. Top with the spinach, onion, and tomato. Broil for 3 minutes.
Remove from the oven and place a couple eggplant slices on top and a little more mustard, if desired.