Heat oil in a large pan over medium-low heat. Add mustard seeds and cook for 30 seconds or until they start to pop. Add curry leaves and onion and stir for 3-5 minutes until onion softens. Add ginger, garlic, curry powder and spices, then cook, stirring, for 1-2 minutes until fragrant.
Step 2
Add coconut milk and 200ml water and bring to a simmer. Reduce heat to low and simmer for 3-5 minutes until slightly thickened. Add beans, tomato, sugar and lime and simmer for a further 2-3 minutes until tomato has softened slightly. Stir through chopped coriander. Serve with rice and naan, garnished with extra coriander.