Savory Herb-Stuffed Onions

Prepare grill for direct grilling. Spray both sides of zucchini slices with cooking spray. Grill on uncovered grill over medium coals 4 minutes or until tender, turning once. Remove; cool. Cut into bite-size pieces; set aside.

Thread mushrooms onto metal skewers. Grill on covered grill over medium coals 20 to 30 minutes or until tender. Remove; coarsely chop. Set aside.

Remove stem and root ends of onions, leaving peels intact. Spray onions with cooking spray; grill, root end up, on covered grill over medium coals 5 minutes or until lightly charred. Remove; cool slightly. Peel and scoop about 1 inch of pulp from stem ends; chop pulp for filling.

Combine zucchini, mushrooms, onion, tomato, bread crumbs, basil, oil, salt and pepper in large bowl; mix until well blended. Spoon equal amounts of stuffing mixture into centers of onions.

Place each onion on sheet of foil; sprinkle each with 1 tablespoon water. Wrap onions; seal foil. Grill onion packets on covered grill over medium coals 45 to 60 minutes or until tender. Spoon 1 teaspoon vinegar over each onion before serving.