Preheat the oven to 220C/200C Fan/Gas 7 and put two baking trays in to heat.
To make the sauce, put the tomatoes, mixed herbs and sugar in a saucepan. Peel and finely grate the garlic, add it to the pan and set over a medium heat. Simmer gently for 10 minutes until thickened then remove from the heat and season with salt and pepper. Leave to cool.
To make the dough, combine the flour, baking powder and salt in a bowl and make a well in the middle. Pour in the yoghurt the stir with a fork to combine. When the mixture forms a rough dough, turn out onto a lightly floured work surface and knead to form a smooth ball. Divide the dough into 4 equal pieces and roll out into thin circles.
Carefully remove the hot baking trays from the oven and lay the pizza bases on top. Bake for 3-4 minutes until beginning to rise then remove from the oven.
Turn the pizza bases over and top with the sauce. Scatter the mozzarella over the top. Season with black pepper, sprinkle over a pinch of herbs then return to the oven. Bake for 5 minutes until the bases are crisp and the cheese is bubbling.