Mix together the bread flour, baking powder and salt, then gradually pour in the oil and 275ml warm water. Bring together into a ball and lightly knead for 10 minutes.
Place the 100g rocket, 50g pistachios, the lemon, garlic and olive oil in a food processor and blend. Season to taste and set aside.
Cut the flatbread dough into 4 equal pieces and roll each out to a wide circle about 3-4mm thick. Heat a wide heavy pan over a medium heat and cook each flatbread for 3-4 minutes on each side, until golden brown and slightly puffed up. Keep the raw dough covered while you cook and keep the cooked flatbreads warm by covering them in a tea towel.
Meanwhile, heat a griddle pan with ½ tbsp oil over a high heat and add the courgette strips. Cook briefly on each side until there are griddle marks all over and the courgette is just cooked through.
Roughly chop the remaining pistachios. Divide the pesto between the flatbreads and spread evenly, then top with the griddled courgettes, reserved rocket and pistachios.