Blend or process the garlic, chilli, ginger and sugar into a paste. Add the olive and sesame oils, soy sauce and lime juice. Put the prawns in a shallow glass or ceramic dish. Pour the marinade over the top. Cover and marinate in the refrigerator overnight.
Soak bamboo skewers in cold water for at least 30 minutes to prevent them burning. Thread the skewers with the prawns, tomatoes and cucumber. Grill or barbecue for a few minutes until the prawns are pink and cooked through.
Arrange on a platter, and garnish with coriander leaves. Serve hot.