To make the salsa, place all ingredients in a bowl. Toss to combine. Set aside.
To make prawns, process garlic, chilli, coriander/cilantro roots, green onion, sugar, fish sauce, and lime juice until smooth.
Preheat a lightly greased barbecue plate on medium-high heat. Cook prawns, tossing, for 3-4 minutes or until pink and cooked through. Transfer to a bowl. Add garlic mixture. Toss to combine. Serve prawn mixture, with mango salsa and lime wedges.