Spray a nonstick grill pan with the cooking spray and heat over medium heat for 1 minute.
Add the mushrooms, pepper and onion to one side of the pan.
Add the eggplant to the other side.
Sprinkle the garlic powder over all, if desired.
Cook until the vegetables are tender.
Sprinkle the eggplant with the cheese and cook until the cheese is melted.
Place the mushrooms, pepper and onion into a medium bowl.
Add the vinegar and toss to coat.
Divide the eggplant slices among 4 bread slices.
Top with the mushroom mixture and remaining bread slices.
Alternate Preparation: If you don't have a grill pan, this recipe can be made in a 12-inch nonstick skillet.
Send your little ones to school with this nutritious and easy lunch box meal - a Pan Grilled Veggie and Cheese sandwich.