Heat the oil in a large wok or frying pan. Add the onion and stir-fry for 5 minutes. Add the red pepper and mange tout, and cook for a further 2 minutes.
Stir in the lamb and the arrabbiata sauce and bring to a simmer. Cook for 5 minutes.
Meanwhile, prepare the couscous to pack instructions. Stir into the spicy lamb mixture and serve with the toasted pitta.