Heat the vegetable oil in a deep frying pan and tip in the paste. Cook gently for 15 minutes or until the shallot no longer smells raw. Tip in the coconut milk, pineapple and kaffir lime leaves, and simmer gently for 10 minutes. Stir in the prawns and cook gently for 5 minutes or until they just turn pink. Season with the fish sauce and lime juice. Sprinkle over the red chillies and crispy onions, and serve with rice.