Whisk together the zest, and juice of orange, ¼ cup olive oil, and garlic together in a small bowl. Set aside.
Brush tomato, and onions slices with olive oil. Grill the tomato and onion slices 2 – 3 minutes on each side, or just until charred and softened.
Arrange tomato, onion, & mozzarella slices in rows, overlapping slices on a serving platter. Garnish with fresh basil, drizzle with the orange dressing and serve.