Preheat your oven to 200°C (400°F) and line a large rimmed baking sheet with parchment paper or lightly oil it.
Chop the zucchini, eggplant, and bell peppers into roughly 1-inch pieces, keeping them uniform for even roasting. If using larger cherry tomatoes, leave them whole or halve them.
Place all the chopped vegetables and cherry tomatoes in a big mixing bowl. Drizzle with olive oil, sprinkle with dried thyme, salt, and pepper, then toss everything together until evenly coated.
Spread the coated vegetables out in a single layer on the prepared baking sheet, making sure they aren’t crowded—this helps them caramelize better.
Roast in the oven for about 25 to 30 minutes, stirring halfway through, until the vegetables are tender, browned at the edges, and smell fragrant with caramelized notes.
Remove the sheet from the oven and squeeze fresh lemon juice over the vegetables for brightness. Toss gently to combine.
Transfer the roasted ratatouille to a serving dish, drizzle with a little extra olive oil if desired, and garnish with fresh herbs for extra flavor.