Preheat oven to 400 degrees f.
Line a large baking sheet with parchment paper.
Slice zucchinis in half the long way. Spoon out seeds, just slightly. Pat the insides dry with paper towels (very important). Sprinkle with sea salt, pepper, and garlic powder, very lightly.
Spoon 1-2 Tbsps marinara sauce over each zucchini, leaving a small rim near edges. Sprinkle tops evenly with mozzarella cheese then with parmesan cheese.
Bake in preheated oven for 6 minutes, then remove from oven, and place tomato halves onto the melted cheese.
Return to the oven, and continue baking for 6-7 minutes. (bake time will vary depending on how thick your zucchini are and how crisp/tender you want them)
Remove from the oven and sprinkle with fresh chopped basil. Serve hot.