Heat the oil in a pan, add onion and fry until they colour. Crush the garlic into the pan, add ginger and chilli; cook briefly. Add tomatoes and a quarter of a can of water and bring to the boil. Simmer for 2 mins, add prawns or chicken and gujarati masala, cover and cook for 2-3 mins for prawns and 5-6 mins for chicken.
Reduce the heat to a simmer, then stir in the yogurt, a tablespoonful at time. Sprinkle with coriander and serve with warm garlic and coriander naans and a crisp salad of cucumber, shredded lettuce, sliced red onion and wedges of lemon.