Thinly slice the beef against the grain and marinate beef with oyster sauce, dark soy sauce, salt, pepper, garlic and 2 teaspoons of olive oil for 5-10 minutes.

Cut the red bell pepper in half length-wise, remove all the seeds and slice into 0.25'' thick strips.

Trim off the top and bottom of the onion, peel off the skin, cut into half length-wise and slice thinly.

Wash and pat dry Thai basil, discard all the stems. We only use the leaves in this recipe.

Put a pan on the stove on medium high heat. When it's hot enough, add olive oil to the pan, then add red bell pepper strips and onion half rings. Saute bell pepper and onion for about 2 minutes, stirring frequently then add a pinch of salt and pepper. Saute for another minute until bell pepper is quite tender and onion has developed colors. Transfer both to a bowl, set aside.

Increase the heat to medium high-high, wait about 30 seconds for the pan to be hot enough and add the beef in one layer. Leave the beef on the pan undisturbed for 30 seconds and then start stir frying.

After the beef has been 75% cooked (this shouldn't take long, probably just another minute), add bell pepper and onion back to the pan, add fish sauce, soy sauce, adjust seasoning to your liking and stir fry everything together until beef is fully cooked. Again, this shouldn't take long at all, a minute or so.

Turn off the heat, remove the pan from the hot stove and add basil to the pan. Quickly mix the basil into the dish and then transfer immediately to a clean plate.

Serve hot with rice.