Stir fry beef with onion

Ingredients:
AAA Flank beef 500g (cut them against the grain into small and thin slices. AAA beef is more tender.)
Onion-1 big one
Chili-2

Marinating sauce:
Soy sauce-2 teaspoons
Corn starch-2 teaspoons
Extra virgin olive oil-1 teaspoon

Seasoning:
Salt
Black pepper

Method:

1. Marinate beef with marinating sauce for 20 mins.
2. Cut onion into slices and chop chillis
3. Add one teaspoon of extra virgin olive oil in to the pan. Wait until it's heated, cook beef with high heat. (one way to test if the pan is hot enough is to use a bamboo chop stick to dip into the oil. If you can see the bubbles, it means it's hot enough) Quickly, stir the beef around. Cook until medium rare, then take them out.
4. Add one teaspoon of extra virgin olive oil and cook onion for 5-6 mins or until they become soft.
5. Add the chillies and the beef back. Quickly stir them around.
6. Add salt and black pepper (As soon as the beef isn't red, take them out. Don't overcook beef, they will be tough.)
7. Serve