Creating Authentic Filipino Beef Steak (Bistek Tagalog) can be simple if you follow these steps:

1. Marinate the Beef: In a bowl, combine the beef slices, soy sauce, calamansi juice, and minced garlic. Let it marinate for at least 15 minutes.
2. Prepare the Onion: While the beef is marinating, slice the onions into rings and set them aside.
3. Heat the Oil: In a large skillet, heat the vegetable oil over medium heat.
4. Cook the Beef: Remove beef from the marinade, reserving the marinade for later. Sauté the beef in the hot oil until browned, about 3-5 minutes. Remove the beef from the skillet and set aside.
5. Sauté the Onion: In the same skillet, add the onion rings and cook until they become translucent, about 2-3 minutes.
6. Combine Ingredients: Return the browned beef to the skillet. Pour in the reserved marinade and add 1 cup of water. Bring to a boil.
7. Simmer: Reduce the heat to medium-low and let it simmer for about 15-20 minutes, allowing the flavors to meld together.
8. Season to Taste: Taste and adjust the seasoning with salt and pepper as needed.
9. Serve: Once cooked, transfer to a serving dish and garnish with green onions if desired.

These steps will ensure that your Bistek Tagalog turns out delicious and authentic!