Preheat the oven to 180 degrees Celsius. Place the tomatoes on a baking tray lined with baking paper. Brush lightly with olive oil and bake for 40-50 minutes.
While the tomatoes are roasting, put the onions in a pan with the balsamic vinegar, water and sugar. Bring to a boil over a medium heat before reducing the heat and simmering until the onions are very soft, tender and sweet.
When the tomatoes are cooked, reduce the oven to 150 degrees. Line the bottom of the pastry shell with the onions and herbs. Arrange the olives on top, then cover with the roasted tomatoes, and goat's cheese.
Warm in the oven for 10 minutes and serve with the Italian green salad.