Preheat your oven to 400°F (200°C). Line your sheet pan with parchment paper for easy cleanup.
Wash and slice the zucchini into rounds, about 1/4 inch thick. Slice the bell peppers into strips, removing the stem and seeds. Cut the eggplant into rounds similar to the zucchini. Slice the onion into rings.
Place all the sliced vegetables into a mixing bowl. Drizzle with olive oil, then sprinkle with dried thyme, oregano, salt, and pepper. Toss gently to coat everything evenly with the oil and herbs.
Spread the seasoned vegetables evenly across the prepared sheet pan in a single layer, mixing the different colors and shapes for a vibrant look.
Scatter the cherry tomatoes across the top of the vegetables. The tomatoes will burst slightly during roasting, adding sweetness and moisture.
Place the sheet pan in the oven and roast for about 25 minutes, or until the vegetables are tender, caramelized at the edges, and fragrant. Shake or stir the vegetables halfway through cooking for even roasting.
Remove the sheet pan from the oven and let the vegetables cool slightly. They should be soft, with a slight char for added flavor.
Serve the roasted vegetable ratatouille warm, enjoying the colorful, tender, and flavorful medley that’s ready to be enjoyed as a main or side dish.