1.Cut base from lemongrass stalks; remove tough outer leaves then trim each stalk to approximately 22cm in length.
2.Peel and devein prawns, leaving tails intact. Make marinade by whisking lime juice, oil and chilli together in a bowl; stir in peeled prawns then cover and refrigerate for 30 minutes. Remove prawns from marinade, reserve marinade.
3.Cut a small slit through centre of each prawn, then thread tails through slits so prawns are circular in shape. Cut bacon into approximately 3cm squares and pierce a small hole in the centre of each square. Thread prawns and bacon alternately onto lemongrass stalks.
4.Cook on a heated greased barbecue plate, brushing occasionally with reserved marinade, until prawns are tender and bacon is crisp. Serve with lime wedges, if desired.
Lemongrass stalks are available from greengrocers or the fruit and vegetable section in most supermarkets. If unavailable, use bamboo skewers instead. Prawns and bacon can be threaded onto lemongrass skewers several hours ahead. Keep covered in the refrigerator and barbecue as required.