In medium saucepan, cook zucchini and onions, covered, in boiling water to cover for 1 minute.
Remove with slotted spoon and drain.
Alternately thread zucchini, onions and mushrooms on 4 skewers.
Brush with melted butter.
Grill vegetables, on covered grill, over medium-hot Charcoal Briquets 6 minutes or until tender, carefully turning skewers once.
Add cherry tomatoes to end of skewers during last minute of grilling.
Season to taste with salt and pepper.