Heat the olive oil in a frying pan, add the onion, garlic and fennel and cook for 3 minutes. Add the tomatoes, sugar and tomato purée and simmer for 5 minutes until the mixture is soft and pulpy. Season with salt and pepper.
Meanwhile, make the pizza base according to the instructions on the packet. Knead lightly until smooth, shape into a ball and roll out thinly to a circle about 30 cm (12 inches) across. Place on a baking sheet.
Spread the tomato and fennel sauce over the pizza base and scatter over the chicken and cherry tomatoes. Arrange the mozzarella on top and bake in a preheated oven, 220°C (425°F), Gas Mark 7, for 15 minutes until crisp and golden.