Lightly season prawns with seafood seasoning and set aside in a medium bowl.
In a two litre saucepan, combine mango juice concentrate, butter, lemon, sugar, cinnamon, lemongrass paste, paprika over medium heat and bring to a boil. Reduce heat and simmer for 15 minutes or until sauce thickens enough to coat the back of a spoon. Let cool.
Pour half of the sauce over the prawns, cover with plastic wrap and transfer to the refrigerator to marinate for one hour (could be done a day in advance). Reserve remaining sauce for basting.
Preheat barbecue grill. Remove the tough outer layers from lemongrass stalks and discard. Beat stalks a few times with a mallet to release their fragrant oils.
Toss lemongrass stalks with oil. Grill for about one minute on each side for grill marks to appear. Set aside on a plate and let cool.
Thread three to four shrimps onto each stalk and grill while basting on both sides with reserved sauce until opaque, about two to three minutes per side. Transfer to a platter, garnish with coconut and cilantro and serve at once.