For the dough: mix together the flour, salt, sugar and yeast in a large bowl. Stir in the oil and water to form a soft dough. Transfer to a lightly floured surface and knead dough for 10 minutes. Return to a bowl. Cover with a tea towel and leave in a warm place for about 1-1/2 hours until well risen and double in volume.
Meanwhile for the tomato sauce: heat the oil in a saucepan and sauté the onion for 5 minutes, until softened. Stir in the garlic and cook for 2 minutes. Stir in the remaining ingredients, bring to the boil and cover and simmer for 10-15 minutes, until thickened. Remove from the heat and allow to cool.
For the topping: Heat the oil in a frying pan and cook the peppers for 10 minutes, over a medium heat, stirring occasionally until softened. Remove from the heat and allow to cool.
Divide the dough into four and roll into balls on a floured surface. Cover with a damp tea towel and leave to rise for 10-20 minutes. Roll out each to a 23cm circle. Place on baking sheets and leave for 10 minutes.
Preheat oven to 220C/fan 200C/Gas 7. Divide the tomato sauce between the pizza bases spreading over evenly and leaving a 1cm gap around the edge. Then top the pizzas with the prepared peppers, Boursin Minis and remaining topping ingredients except the rocket. Bake for 10-12 minutes, until cheese is melted. Serve immediately scattered with rocket.