In a wide bowl, combine lemon juice, soy sauce, brown sugar, pepper and garlic. Whisk to combine and to dissolve the sugar. Add beef to the marinade and mix or toss to coat every piece of the beef. Let it marinate for at least 30 minutes. (overnight if you are not in a hurry) Drain the beef and set aside remaining marinade for later use.
Heat a wide pan over medium-high heat and add cooking oil. Add onion rings and cook for about 30 seconds or cook according to preference. Remove onions from oil and set aside.
Using the same pan with oil, fry beef by batches for about 3-5 minutes total. Cook until lightly browned then transfer beef in a plate and set aside.
Pour-in remaining marinade to the same pan. Simmer over low heat for about 3 minutes stirring once. Return fried beef to the pan and gently stir to combine. Let it simmer for about 5 minutes or until sauce thickens.
Top with fried onions and cook for another minute. Transfer Bistek Tagalog in a serving dish and serve warm with steamed rice. Enjoy!
