1. Cut the meat into thin strips.
2. Marinate it for 1 hour with soy sauce, sesame oil, and fish sauce.
3. Peel and slice the onions.
4. Heat some oil (sunflower or canola) in a large skillet or wok.
5. Add the beef and onions and cook over high heat until browned.
6. Add the sweet soy sauce and cook until the onions are tender.
7. Season with salt and pepper, and serve with Thai or basmati rice.