Wash the lamb neck and pat it dry with paper towels. In a medium bowl, mix together the pineapple juice, vinegar, sugar, and adjust the seasonings with salt, and pepper. Transfer the lamb to a bowl and pour over half of the marinade. Cover the bowl with plastic wrap, and set the meat in the refrigerator to marinate for 1 hour or up to 4 hours.
Soak the wooden skewers in cold water for at least 30 minutes prior to cooking the kebabs. The water will help prevent them from burning.
Dice the bell peppers and onions into 1 1/4-inch cubes. Using a sharp knife, remove the skin from the pineapple, quarter the fruit lengthwise and discard the hard central core from each piece. Cut the pineapple flesh as well as the banana into similar-sized chunks. Thread the bell peppers, onions, pineapple, banana, and lamb evenly on to the soaked skewers to make 10 to 12 generously laden kebabs.
Heat a griddle pan over high heat or preheat a grill to medium-high heat and lightly oil the grates, or preheat the broiler. Brush the kebabs with some oil. Place the kebabs onto the grill, turning frequently, and using the remaining marinade for basting. They should be done after around 10 minutes, turning frequently.