Instructions:

1. Marinate the beef:
In a bowl, combine the sliced beef with 1 tbsp soy sauce and 1/2 tsp ground cumin. Mix well and let it marinate for at least 15 minutes.

2. Heat the oil:
In a large skillet or wok over high heat, heat the vegetable oil.

3. Cook the beef:
Add the marinated beef to the skillet and stir-fry until browned on all sides. Remove the beef from the skillet and set aside.

4. Sauté aromatics:
Add the garlic, ginger, and cumin seeds to the skillet and cook for about 30 seconds, or until fragrant.

5. Add onion:
Add the sliced onion to the skillet and stir-fry for 2-3 minutes, or until softened.

6. Return beef to skillet:
Add the cooked beef back to the skillet and mix well with the onions.

7. Season the stir-fry:
Add the remaining soy sauce, oyster sauce, red pepper flakes, and salt and pepper to taste. Stir-fry for another 1-2 minutes to combine flavors.

8. Garnish and serve:
Garnish the stir-fry with fresh cilantro, if desired, and serve hot with rice