Finely slice the clean vegetables using a mandolin cross or lengthwise. Lightly oil a round oven-proof dish. Starting from the outside, arrange the vegetables around the dish in an upright position, alternating colors and pressing them in tightly. This task may require extra patience or a third hand to help. Alternatively, use a square dish or arrange vegetables in rows, or layers like lasagna. There’s no wrong way of layering.
Tuck garlic pieces between the vegetable rows. Drizzle with oil, season with salt and pepper, and top with thyme. Bake uncovered until vegetables are tender, about 50-60 minutes. Serve warm or at room temperature garnished with torn basil leaves.
You can also use yellow squash and sautéed onions if you like. I added sliced mushrooms into the empty spaces between the vegetables.