The summer side you can make whenever you have 15 minutes, and then completely forget about. Because the zucchini is already cooked through and relaxed, the marinade seeps in more quickly and thoroughly than had the order of operations been reversed. The zucchini boats become bright and aromatic, but hang onto their fresh structure and sweetness. It's just about the simplest, best summer side, whether you're serving it to a dinner party, your family, or just you. From Canal House Cooking Volume No. 8: Pronto (Andrews McMeel Publishing, 2013).
Working in batches as needed, heat 2 tablespoons of olive oil in a heavy medium skillet over medium-high heat. Arrange the zucchini cut side down in one layer in the hot skillet and cook until browned, about 3 minutes. Use a fork or tongs to turn the zucchini over, then cook them until tender, about 2 minutes, reducing the heat if the zucchini get too dark. Transfer the zucchini to a shallow dish and sprinkle with salt.
Whisk together the garlic, vinegar, and remaining 3 tablespoons of olive oil in a small bowl. Season with salt and pepper. Pour the vinaigrette over the zucchini and add the basil. Gently toss everything together and adjust the seasonings. Let the zucchini marinate at room temperature for about 1 hour before serving. Alternately, let marinate longer in the refrigerator. Tightly covered, marinated zucchini will keep for up to a week in the refrigerator.