To Grill: Prepare grill. Spray grill rack with no stick cooking spray. Using direct heat cooking method, arrange skewers on grill rack 5 inches over hot coals. Grill kabobs, covered, until scallops and shrimp are opaque throughout (3-4 minutes per side), brushing and turning often. (The skewers are easiest to turn with long-handled tongs. Avoid clamping onto onions, as they tear easily.)