Heat some olive oil in a saucepan over medium heat, sauté the onion and garlic.
Add the chopped red pepper and sauté until soft.
Add the diced tomatoes and tomato purée. Stir well and simmer on a low heat for approx. 15-20 minutes.
Add the herbs and season with salt and pepper. Add sugar if desired and mix together. Allow the sauce to cool slightly while you prepare the ratatouille.
Prepare the ratatouille
Preheat the oven to 180 degrees Celsius / 356 Fahrenheit top and bottom heat.
Pour the tomato sauce into the oven dish. Arrange the slices of zucchini, eggplant and tomato in a tiled pattern in the oven dish. Alternate the different vegetables to create an attractive pattern.
Drizzle the vegetables with some olive oil and sprinkle them with the herbs, salt and pepper to taste.
Bake the ratatouille for 35-40 minutes, or until the vegetables are tender and starting to brown.
Serve the ratatouille with delicious bread, such as French bread, a salad and/or baked potatoes. Bon appetit!