Start by finely chopping the onions and garlic. In a cast iron pot, such as a Staub or Le Creuset, heat a drizzle of olive oil over high heat. Add the onions and garlic, letting them sweat and caramelize uncovered.
While they cook, wash and finely chop the tomatoes, zucchinis, and bell peppers into small, even pieces.
Once the onions and garlic are golden and fragrant, reduce the heat to medium-low and add the chopped vegetables to the pot. Stir well, drizzle a little more olive oil, and sprinkle in the Herbes de Provence. Mix everything thoroughly to combine the flavors.
Cover the pot with its lid and let the ratatouille simmer gently over low to medium heat for about 45 minutes, stirring occasionally to ensure even cooking.
When the ratatouille is ready, season to taste with salt and freshly ground black pepper. Serve immediately, and don’t forget to pair it with a crusty French baguette to mop up the delicious sauce. Bon appétit!