Saute the onion in oil, add the tomatoes, cut them into slices and let them simmer for 2-3 minutes. Pour the mixture into a tall container, add the cheese, basil, mayonnaise, salt and pepper to taste.
Spread the dough in a baking dish with slightly raised edges. Pour the tomato mixture in. Brush the edges of the dough with a little egg, bake in a preheated oven for 20-35 minutes.
Garnish with fresh basil leaves and serve with a green salad.