Preheat your oven to 200°C (400°F) and line a large rimmed baking sheet with parchment paper. Arrange all the sliced vegetables on a cutting board or tray for easy assembly.
In a small bowl, mix the olive oil with thyme, salt, and pepper. Brush or toss the sliced eggplant, zucchini, peppers, and tomatoes with this mixture until evenly coated.
Spread the vegetables in a single, even layer on the prepared baking sheet. Make sure not to overcrowd them to promote caramelization.
Place the sheet in the oven and roast for about 25-30 minutes, until the edges are golden and slightly charred, and the vegetables are tender when pierced with a fork. Toss the vegetables gently with a spatula halfway through to promote even browning.
Once roasted, remove the sheet from the oven and let the vegetables rest for 5 minutes to settle the flavors and cool slightly.
Transfer the roasted vegetables to a serving dish or bowl. Garnish with fresh basil leaves for a bright, fragrant finish.
Serve your roasted ratatouille warm or at room temperature, enjoying the smoky aroma and tender, caramelized textures.