Combine cumin and garlic; press onto beef steaks. Place steaks on grill over medium, ash-covered coals. Grill, uncovered, 15 to 18 minutes for medium rare to medium doneness, turning occasionally. (Or to broil, place steaks on rack in broiler pan so surface of beef is 3" to 4" from heat. Broil 13 to 17 minutes for medium rare to medium doneness, turning once.)
Squeeze lime wedges over steaks. Carve steaks; season with salt. Serve with guacamole.