Preheat the grill to medium heat.
In a large bowl, toss the zucchini slices with olive oil, salt, and black pepper until evenly coated.
Place the zucchini slices on the grill and cook for about 3-4 minutes on each side, or until grill marks appear and the zucchini is tender. Remove from the grill and let cool slightly.
On a serving platter, layer the grilled zucchini, mozzarella slices, and tomato slices, alternating each ingredient.
Tuck fresh basil leaves between the layers.
Drizzle balsamic glaze over the top of the stackers before serving.