Place a grill pan over high heat on your stove.
Brush olive oil all over the onions and the eggplant and the red onions. Season with salt and pepper.
Once the grill is hot add the slices of eggplant and red onion and grill for about 5 minutes each side. Brush more oil if it gets a bit dry and turn once over again.
Place 5 to 6 slices of shaved zucchini on the place. Drizzle with a very small amount of olive oil and sprinkle salt and pepper.
Top it with one slice of tomato and start layering the eggplant, mozzarella, red onion, mozzarella, eggplant.
Sprinkle salt and pepper all over the stack of vegetables. Drizzle olive oil and balsamic vinegar.