Roast the eggplant: Preheat the oven to 350°F. Cut the eggplant in half lengthwise, then score the cut sides in a half-inch crosshatch pattern. Brush each side with 3 tablespoons olive oil, season generously with salt and pepper and arrange the eggplants, face down, on a rimmed baking sheet. Roast until the eggplant i soft and the undersides are golden, 20 minutes.

While the eggplants are cooking, make the sauce: Heat the remaining 2 tablespoons olive oil in a small saucepan over medium heat. Add the garlic and cook 1 additional minute. Add the crushed tomatoes, basil, Italian seasoning, chili flakes, and salt, bring to a boil, reduce the heat and simmer until the sauce thickens, 15 minutes.

Top and finish the dish: Remove the eggplant from the oven but leave the oven on. Use a spatula to flip the eggplant, then divide the sauce among the 2 eggplant halves. Divide the mozzarella among the eggplant halves and bake until the cheese is bubbly 10 minutes. Remove from the oven and garnish with basil.