Marinate chicken in lime, garlic and salt, we did overnight. Fry onion and stir in marinated chicken. Add diced tomatoes and peanut oil and let cook for 10 minutes. Add shrimp paste and coconut milk and simmer gently for another 10 minutes. Add coriander, cashew nuts and prawns and cooked until prawns are done. Sir in chillies if using and serve. We served with rice.