In a bowl, combine beef, lemon juice, soy sauce, onions, garlic and pepper. Massage marinade into meat and marinate for about 30 minutes.
In a cast iron wok, over high heat, heat oil. Add beef and cook for about 3 to 5 minutes per side or until lightly browned. Remove meat.
In the pan, add onions and garlic (from marinade mixture), and cook, stirring regularly, until limp and aromatic. Return meat to pan.
Add reserved marinade. Add water and bring to a boil. Cover, lower heat and simmer for about 40 to 50 minutes or until meat is fork-tender and liquid is reduced.
Season with salt to taste.
Turn off heat.
Garnish with onion rings (optional) and cover to allow onion to cook slightly in the steam.
Serve hot.