Thread beef and capsicums onto skewers. In a bowl whisk marinade ingredients together. Brush marinade over skewers, then place on a lined baking tray and leave to marinate in the fridge for at least 30 minutes. Reserve marinade for basting.
Whisk salad dressing in a small jug until well combined. Place all prepared salad ingredients in a serving bowl and toss with salad dressing.
Preheat the barbecue or grilled pan to high. Cook the skewers for 10 minutes, turning and brushing with remaining marinade every few minutes, until beef is browned and cooked to your liking. Serve hot with extra Lee Kum Kee Char Siu Sauce drizzled over and the cucumber salad served on the side.