If you are using wooden skewers, begin soaking them in water to prevent burning on the grill.
Combine jalapeno, garlic, olive oil, lime juice, salt and cumin together in a food processor. Process until well blended.
Place prawns in a bowl. Pour jalapeno garlic mixture over the top. Mix well. Cover and refrigerate for 20 minutes.
Skewer 5 - 6 prawns per skewer. Pour any remaining mixture over the prawns. Grill over medium heat 3 - 4 minutes or until prawns are pink and cooked through. Serve immediately.