Sift the flour into a bowl. Add the yeast to one side and the salt to the other side. Add 2 tablespoons of the oil and the measurement water and mix to form a dough, adding a little more water if the dough seems dry.
Tip the dough on to a lightly floured surface and knead for 10 minutes until smooth and stretchy. Put the dough in a clean bowl, cover with clingfilm and leave to rise in a warm place for about 1 hour until doubled in size.
Turn the dough out on to a lightly floured surface and knead lightly for 1 minute. Press or roll the dough out to a rough oblong about 1 cm (½ inch) thick and place on a lightly oiled baking sheet. Loosely cover and leave to prove for 20 minutes.
Meanwhile, heat 1 tablespoon of the remaining oil in a frying pan, add the onion and cook over a medium heat for about 3 minutes until just softened. Add the courgette and chilli and cook for a further 3 minutes. Set aside.
Press indentations with your fingertip into the dough surface. Drizzle over the remaining oil and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes. Scatter over the vegetable mixture with the salt flakes and rosemary sprigs and bake for a further 10–15 minutes until golden. Cool on a wire rack.