Heat the oil in a large nonstick pan or wok. Add the onion and cook for 2 minutes.
Add the red pepper and celery and sauté for a few minutes. Add the soy sauce, tomato ketchup and chilli powder and stir well.
Add the remaining vegetables and stir-fry over a medium heat for 10–15 minutes until the vegetables are tender. Add a small amount of water if necessary.
Garnish the stir-fry with spring onion curls (if liked) and serve with wholemeal pitta bread.