Peel prawns removing all shell, back vein and rinse thoroughly.
To make the marinade, place jalapeño, lime juice, garlic, olive oil, chilli powder, salt, and lime zest in a blender. Blend into a puree until garlic and jalapeño are completely chopped.
Place prawns in a large snap lock bag. Pour marinade in and toss to combine. Let marinade set at room temperature for 30 minutes while preparing the grill.
Light one chimney full of charcoal. When all the charcoal is lit and covered with grey ash, pour out and spread the coals evenly over entire surface of your fire grate. Set cooking grate in place, cover grill and allow to preheat for 5 minutes, or until it reaches medium-high heat. Clean and oil the grilling grate.
Grill prawns over high heat until just cooked through, about 2-3 minutes per side. Remove to a platter and serve immediately.