Heat 1 tbsp of oil in a pan, then cook the garlic, ginger, chilli and lemon grass for a couple of minutes. Add the spices and cook for a minute, then tip in the tomatoes, tamarind and 600ml water and simmer for 5 minutes. Blend until smooth. Heat up again and add the rice, and then simmer for 10-12 minutes or until the rice is cooked.