In a bowl, combine the thinly sliced beef, soy sauce, lemon juice, minced garlic, and ground black pepper. Mix well to ensure the beef is evenly coated with the marinade. Let it marinate for at least 30 minutes to allow the flavors to meld.

In a large skillet or frying pan, heat the cooking oil over medium heat.

Once the oil is hot, add the marinated beef slices in a single layer. Sear them for about 2-3 minutes on each side until they are browned and cooked through. You may need to do this in batches to avoid overcrowding the pan.

Remove the seared beef from the pan and set aside. In the same pan, add the sliced onions and lemon rounds. Cook them for about 2 minutes until the onions are translucent and the lemon slices are slightly softened.

Pour in the water to deglaze the pan, scraping off any browned bits stuck to the bottom. This will add extra flavor to the sauce.

Return the seared beef to the pan, nestling them among the onions and lemon slices.

Lower the heat to medium-low and let the beef simmer in the sauce for about 5-7 minutes, allowing the flavors to meld together and the sauce to slightly reduce.

Once the beef is cooked through and the sauce has thickened slightly, remove from heat. Serve hot over steamed rice, garnished with additional lemon slices if desired.

Enjoy your delicious Filipino beef steak!