Wash and dice the eggplant, zucchini, bell peppers, and tomatoes into uniform bite-sized pieces. Chop the yellow onion and mince the garlic. Preheat the oven to 375°F (190°C).

In a large skillet over medium heat, add a drizzle of olive oil. Toss in the chopped onion and minced garlic, sautéing for about 3-5 minutes until fragrant.

Add the diced eggplant and bell peppers to the skillet. Cook for another 5-7 minutes, stirring occasionally.

Mix in the zucchini and tomatoes. Season with salt, pepper, and thyme. Cook for 5-8 minutes until tomatoes release their juices.

Transfer the vegetable medley to a baking dish, drizzle with more olive oil and sprinkle fresh basil. Roast uncovered for 20-25 minutes.

Remove from oven, let cool slightly, adjust seasoning, and serve warm, at room temperature, or cold.