Tip all of the base ingredients into a mixing bowl. Pour over 300ml warm water - not too hot. Stir quite hard with a spoon until the mixture comes together.
Turn out onto a lightly floured surface and knead 2-3 times until the mixture forms a ball. Divide dough into 8 equalsize pieces. Take 1 piece, leaving the remainder loosely covered with oiled cling film. Lightly flour the surface again and use a rolling pin to roll out dough into a round about 15cm diameter or as thin as you can. Put pizza on a baking sheet.
Mix together the butter and crushed garlic, then spread a little over the pizza. Tear the mozzarella into thin strips and scatter over. Repeat for the remaining pieces of dough. You should be able to fit 2 pizzas per baking sheet; depending on how many baking sheets you have, you may have to cook in batches.
Heat oven to 240C/fan 220C/gas 9. Bake pizzas for 12-15 mins until crisp and cooked through. Meanwhile, mix together the remaining ingredients, then season well. When the pizza comes out of the oven, top with the tomato mixture and serve straight away.