IF you are going to introduce a variation on fast food then the alarm clock becomes as important a utensil in the kitchen as a frying pan. Just ask Californian David Monson (above) - reputedly the tallest chef in Asia - who is promising customers partaking of the ''Fast & Light Lunch'' at the Kowloon Shangri-La's Napa Restaurant that they'll get their money back if their main course is not served within 30 minutes of ordering. With a bargain like that on offer you can be sure it won't be just Monson's alarm that will be ticking away around noon.