Heat oil over medium-high heat in a large sauté pan. When hot, add the zucchini slices in a single layer, working in batches if you have to. Cook for about 2-4 minutes, or until the cooked side is golden brown then flip and cook the second side until browned, another 2-4 minutes. Alternatively, you can coat the slices in oil and broil for 5-10 minutes in the oven until browned.
While squash cooks, prepare the marinade: stir together the garlic, basil, salt, pepper, and vinegar in a small bowl.
When the squash is cooked, transfer to a deep plate then top with the marinade, ensuring all the squash is evenly coated. Cover and refrigerate for a minimum of 2 hours.