In a frying pan, heat the sesame and vegetable oils.
Add the chopped onion and chilies and cook just until fragrant.
Add the beef. Cook, stirring, until the meat has soaked up the oil.
Pour in the sauce. Cook over high heat, uncovered, stirring often, until the mixture is quite dry. This step is to allow the flavors to concentrate and to let the sauce caramelize a bit.
Assemble the tacos.
Toast the tortillas in an oil-free pan.
Lay a taco on a plate. Cover with lettuce. Pile on the beef. Add red onions. Sprinkle with toasted sesame seeds and onion leaves. Finally, add some cilantro.
Fold the Korean beef stew taco and bite. Utterly delicious.