Cut potatoes crosswise in half; place in microwavesafe dish with 1 cup water. Cover and microwave on high 10 to 14 minutes or until almost tender, rearranging once. Immediately rinse under cold running water;
Meanwhile, combine cumin and salt and pepper; press evenly onto beef steak. Place steak on grill over medium, ash-covered coals. Grill, uncovered, 16 to 18 minutes for medium rare doneness, turning occasionally. Remove; let stand 5 minutes.
About 5 minutes before steak is done, brush potatoes with some of the vinaigrette. Place on grid around steak. Grill 5 to 7 minutes or until golden brown, turning occasionally.
Carve steak into thin slices. Combine beef, potatoes, beans, cilantro and remaining vinaigrette - toss gently. Serve immediately.