Whisk together first 8 ingredients. Place steak in food storage bag. Pour ½ cup vinaigrette over steak; seal bag. Refrigerate, turning bag occasionally, several hours or overnight. Cover and refrigerate remaining vinaigrette.
To Grill: Remove steak from marinade; discard marinade. Spray grill rack with no stick cooking spray. Using direct heat cooking method, arrange steak on grill rack 4-5 inches above medium-hot coals. Grill, turning once, until meat thermometer registers 140 F for medium-rare (8-11 minutes) or until desired doneness. Let stand 5 minutes; cut into thin slices.
Whisk chives into reserved vinaigrette. Toss 1 tablespoon vinaigrette with tomatoes. Combine spinach, cucumbers, olives and ½ cup blue cheese. Drizzle remaining vinaigrette over greens; toss to coat. Divide salad among 4 dinner plates. Top with tomatoes and steak slices; sprinkle with remaining blue cheese.