Brush the zucchini halves with olive oil. Season lightly with salt and fresh cracked black pepper.
Preheat the grill on medium-high and grill the zucchini covered for 3-5 minutes per side or just until knife tender.
Remove the grilled zucchini to a serving platter cut side up. Season evenly with garlic powder. Top each half with mozzarella cheese and sliced tomatoes in an overlapping pattern. Top with basil and drizzle with olive oil. Season with additional salt and fresh ground black pepper as needed.