Place garlic, onion, chillies, spring onions, thyme, allspice and ginger into the bowl of a food processor; blend until smooth. Season to taste with salt and pepper. Transfer mixture to a large, non metallic bowl, and stir in rum, treacle, and lime rind and juice.
Place chicken in bowl, and turn to coat. Cover, and marinate for 24 hours.
Preheat barbecue for high heat.
Remove meat from marinade, and thread onto skewers. Boil marinade in a small saucepan for at least 3 minutes.
Brush cooking grate with oil, and arrange skewers on hot grate. Slowly cook the chicken until slightly charred and cooked through, brushing with the marinade every time you turn the meat.