Heat the oil in a large, heavy-based casserole over a medium heat.
Add the onion, garlic, celery and red and yellow peppers and cook for 4–5 minutes, stirring frequently, then add the courgette and cook for a further 3–4 minutes.
Add the herbs, spices and rice and stir-fry for 1 minute, coating the rice well in the other ingredients. Stir in the tomato purée, chopped tomatoes and vegetable stock and season with salt and pepper.
Bring to the boil and cover with a tight fitting lid, then reduce the heat and leave to simmer gently for 15–18 minutes until the rice is cooked and the mixture thickened.