Cut the steak into cubes and put into an earthenware bowl. Combine soy sauce, peanut oil, finely chopped onion, crushed garlic and sesame, seeds, pour over meat and leave to marinate for 3 hours. Turn meat from time to time in the marinade. After 3 hours, or longer, drain meat, reserving marinade. Thread 4-5 meat cubes on small bamboo or wooden skewers. Wrap small pieces of aluminium foil around skewer ends to prevent burning. Mix cumin and lemon juice together and brush over meat. Grill satays over the hot coals of the barbecue or under a preheated griller, basting with marinade and turning frequently. Grill satays until tender: 6-8 minutes for rare; 8-10 minutes for medium; 10-12 minutes for well done. Season with salt and pepper before serving.
Note: Bamboo skewers can be bought in barbecue sections of large department stores. To toast sesame seeds, sprinkle into a large, heavy frying pan and cook over a medium steady heat for 2-3 minutes or until well browned. Do not use any oil. Krupek or prawn crisps are available from oriental or health food shops.