In a wok, heat oil over medium heat.
add beef tenderloin and saute for 3 minutes.
add bell peppers and onions and saute for another 2 minutes.
In a bowl, combine together water, sugar, ketchup, vinegar, chili flakes and garlic. Add mixture to wok.
mix ingredients and bring to a boil.
in another small bowl, combine water and cornstarch. pour into the wok.
stir ingredients well and cook until sauce is thick.
remove from heat and serve. enjoy!
Inspired by Yummy.