Place the steak strips in a large mixing bowl and toss with the Korean BBQ sauce. Cover, and allow to marinate in the fridge for at least 2 hours (or overnight).

When ready to prepare the tacos, place the red onion strips in a shallow serving bowl and cover with 50% vinegar and 50% water. Let the onions soak while you work, for a quick pickling that will mellow the harsher notes of the onion.

If the salad or slaw mix is very chunky, give it a quick chop to create smaller pieces that will sit neatly in the taco shell. Stir in the green onions and cilantro (reserve a little cilantro for garnish at the end, if you'd like). Note that you can prep this mix ahead of time and stash in the fridge.

To cook the beef, preheat a large skillet over medium-high heat. The skillet is ready when you flick drops of water onto the surface, and they immediately sizzle and evaporate.

Add the beef to the skillet. If there are extra juices in the bowl, leave them behind. Saute the beef, stirring frequently until fully cooked and slightly caramelized — a light crust is also okay — from the marinade. Remove to a serving dish.

To prepare the tortillas, heat a dry skillet over medium heat and add a tortilla. Let heat for a minute, and then lift with tongs to check the underside. It should be lightly charred in spots. Flip and repeat. Move to a plate and cover with a towel to steam. Continue with the remaining tortillas. If your pan is large enough to accommodate multiple tortillas at once, go for it!

Drain the vinegar solution from the onions.