Pre-heat a non-stick frying pan, add the onion and dry-fry until lightly browned. Add the garlic, celery, mustard seeds and sausage, then stir in the chilli, rice, stock powder and tomatoes.
Add sufficient water to cover the rice, approximately 600ml (1pt), and bring to the boil. Reduce the heat and simmer gently for 20 mins until the liquid has been absorbed and the rice is cooked.
Season to taste with salt and freshly ground black pepper and serve immediately.