Mix together the flour, salt, pepper and Parmesan in a bowl.
Add the yeast to the water and it to fizz and become frothy.
Pour into the flour mix, add the oil and the egg and mix to a soft dough.
Turn onto a floured surface, knead 5 minutes until smooth and no longer sticky.
Cut each tomato into six, cut the mozzarella into 24 chunks.
Divide the dough into 24 pieces, shape each piece into a ball and flatten.
Place a piece of mozzarella and tomato onto each flattened ball, draw the dough over the filling, pinch to enclose, then place on a greased baking tray.
Cover with a greased plastic sheet, eg. a clean pedal bin liner.
Allow to prove at room temperature for 1 hour until dough is springy when pressed.
Heat the oil to 180C in a large saucepan (Test by dropping a cube of bread into the oil, if it rises to the top immediately the oil is hot enough). Fry the doughnuts a few at a time for about 5 minutes until a deep golden.