Partially freeze steak; trim fat from steak. Slice steak diagonally across grain into 1/4-inch-wide strips, and set aside.
Combine lemon grass and next 4 ingredients in a large heavy-duty, zip-top plastic bag; seal bag, and shake well. Add steak to bag; seal bag, and shake until steak is well coated. Marinate in refrigerator 8 hours, turning bag occasionally.
Combine onion, sugar, vinegar, and 1/4 teaspoon pepper in a bowl; cover and chill at least 30 minutes. Stir in carrot and mint.
Remove steak from marinade; discard marinade. Thread steak onto 4 (12-inch) metal skewers.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Place kabobs on rack; grill, covered, 5 minutes or to desired degree of doneness, turning skewers once. Transfer carrot mixture to a serving platter using a slotted spoon; top with steak, and sprinkle evenly with peanuts.