Peel and slice the pineapple lengthways into 8 wedges, then cut out and discard the woody core. Preheat a large griddle pan over a high heat, add the pineapple for 4 minutes, or until charred and bar-marked, turning occasionally, then remove to a board to cool. Meanwhile, halve, deseed and finely slice the peppers lengthways. Add to the griddle for about 3 minutes, or until slightly softened and bar-marked, turning halfway. Peel the garlic and deseed the chillies, then roughly chop and place into a pestle and mortar. Bash with a pinch of salt to a rough paste. Peel, finely chop and add the ginger, then bash until broken down and combined. Place the chilli paste into a large bowl with the prawns and a splash of oil, then mix well. Heat a lug of oil in a large wok or non-stick frying pan over a medium-high heat. Add the prawn mixture and fry for 3 to 4 minutes, or until just cooked through. Meanwhile, chop the cooled pineapple into bite-sized chunks. In a bowl, combine the pineapple juice, vinegar, soy, cornflour and a splash of water, then add to the wok with the chargrilled pineapple and peppers. Bring to the boil, then simmer over a low heat for about 2 minutes, or until thickened and reduced. Pick over the coriander leaves, then serve with steamed rice.