Quarter the tomatoes, remove the cores and scoop out the pulp and seeds. Set out two bowls and chop the flesh of four tomatoes, placing it, together with the pulp and seeds from all of the tomatoes into one bowl. Place the flesh of the other eight tomatoes into the other bowl.
Puree in a blender or food processor and then pass through a sieve. Discard any solids and set the sauce aside.
Wash the cherry tomatoes and cut them in half, season with a little salt and pepper, mix to combine and set half aside for decoration.
Arrange the stuffed flowers in a gratin dish, pour over the tomato sauce and scatter around the reamaining cherry tomatoes. Bake for 20 minutes.
When cooked, garnish with reserved mozzarella and cherry tomatoes and serve.