Preheat your oven to 180°C (350°F). Lightly oil your ovenproof dish to prevent sticking.
Slice the eggplant into 1/2-inch thick rounds, generously sprinkle with salt, and let sit for 15 minutes. Rinse off excess salt and pat dry; this helps reduce bitterness and softens the eggplant.
While the eggplant rests, slice the zucchini into similar 1/2-inch rounds, and cut the bell peppers into strips. Mince the garlic finely.
Layer the eggplant, zucchini, peppers, and tomato slices in your dish, overlapping them slightly in a decorative pattern. Aim for a loose, colorful arrangement that allows juices to mingle.
Drizzle the olive oil evenly over the layered vegetables, then sprinkle with salt, black pepper, and thyme. Tuck in a few sprigs of fresh basil among the layers for fragrant flavor.
Cover the dish tightly with aluminum foil and bake in the oven for 40–45 minutes, until vegetables are tender and edges begin to caramelize. Check halfway and drizzle a little more olive oil if the top looks dry.
Remove the foil during the last 10 minutes of baking to allow the top to brown slightly and intensify the flavors. The vegetables should be soft, bubbling gently, and beautifully caramelized around the edges.
Once out of the oven, let the ratatouille rest uncovered for 5–10 minutes to allow the juices to settle and flavors to deepen.
Garnish with fresh basil leaves before serving. The dish should be vibrant, with caramelized edges, soft vegetables, and a fragrant aroma that beckons you to dig in.
