1. Cut potatoes into 1-1/2" pieces. Place in microwave-safe dish. Microwave, covered, on HIGH 6 to 8 minutes or until just tender, stirring once. Cool slightly.
2. Combine sauce ingredients in 1-cup glass measure. Microwave on HIGH 1-1/2 minutes, stirring once.
3. Cut squash lengthwise in half. Cut beef steak and squash into 1-1/4" pieces. Combine beef, squash, potatoes and 1/3 cup sauce in bowl; toss. Thread beef and vegetables alternately onto metal skewers.
4. Place kabobs on grid over medium, ash-covered coals. Grill, uncovered, about 9 to 11 minutes for medium rare to medium doneness, turning occasionally. Brush with remaining sauce during last 5 minutes.