In a bowl, combine beef, lemon juice, soy sauce, sliced onions, garlic, and pepper. Massage the marinade into the meat and marinate for about 30 minutes.
Remove meat, onions, and garlic from marinade, squeezing and reserving excess liquid.
In a pan over high heat, heat oil. Add beef and cook for about 3 to 5 minutes per side or until lightly browned. Spoon out and reserve released meat juices during frying. Remove meat.
In the pan, add onions and garlic, and cook, stirring regularly, until softened. Return browned beef to pan.
Add reserved marinade and meat juices. 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, if desired, and cover to allow onions to cook slightly in the steam. Serve hot.