Preheat your oven to 200°C (392°F). Line a baking sheet with parchment paper for easy cleanup.
Chop the zucchini, eggplant, and bell peppers into roughly 2-inch chunks, keeping the sizes uniform for even roasting. If using cherry tomatoes, leave them whole or halve if preferred.
Place all the chopped vegetables and cherry tomatoes into a large bowl. Drizzle with about 2 tablespoons of olive oil, add the minced garlic, chopped thyme, salt, and pepper.
Toss everything together gently until all the vegetables are evenly coated with oil and seasoning.
Spread the vegetables in a single layer on the prepared baking sheet, making sure not to overcrowd the pan so they can caramelize properly.
Roast in the oven for 25 to 30 minutes, stirring halfway through, until the edges are golden and caramelized, and the vegetables are tender.
Once roasted, remove from the oven and taste. Adjust seasoning with more salt, pepper, or a squeeze of lemon if desired.
Sprinkle freshly chopped basil over the hot vegetables and gently toss to combine. The basil adds a fresh, aromatic finish.
Serve the sheet pan ratatouille hot, or at room temperature. It pairs beautifully with crusty bread, grains, or as a hearty main.