- Peel then finely chop the onions and garlic. Rinse, de-seed and slice the sweet peppers. Rinse, turn and cut the eggplant into small cubes. Rinse, trim and thinly slice the zucchinis.
- Place the onions, garlic and sweet peppers into a large saucepan. Add tomatoes, stir in the bouquet garni, tomato puree and season to taste.
- Bring to boil, cover and simmer for 10 minutes, stirring half-way through.
- Stir in the prepared eggplant and zucchini then cook, uncovered, for further 10 minutes, stirring occasionally.
- Meanwhile, peel the potatoes and cut into 1 inch cubes. Place them into another saucepan and cover with water. Bring to boil and cook for 10-12 minutes until tender. Drain and set aside.
- Transfer the vegetables to a heatproof gratin dish. Pile the cooked potato cubes evenly over vegetables.
- Preheat the grill to medium. Sprinkle grated cheese over the potatoes, place under grill for 5 minutes until golden, bubbling and hot.
- Serve garnished with chopped chives.