Place the meat in a medium-sized bowl, and add all the ingredients except for the peanut oil.
Let marinate in the fridge for 2 to 12 hours.
Place the coarsely chopped cabbage in a large bowl.
Dissolve the salt in water and pour the solution over the cabbage.
Make sure the cabbage is completely submerged and let soak for at least 1 hour.
Combine the remaining ingredients in a bowl to make the kimchi sauce.
Drain and rinse cabbage and place in a large, clean bowl. Pour the sauce over the cabbage.
Transfer the contents of the bowl to a leak-proof bag and place in simmering water for 30 minutes. (A heavy-duty freezer bag works, just don't let it lay on the side of the hot pan).
Remove and let cool before transferring to a serving vessel.
Heat the peanut oil in a medium skillet over medium high heat.
Add the marinated beef to the pan and cook until medium rare (about 4 minutes), or to medium (about 6 or 7 minutes)
Heat tortillas over a medium flame.
In a medium bowl, mix together the ingredients for the BBQ sauce.
Build the tacos by placing several strips of beef with the sauce. Top with a mound of kimchi, and then drizzle the BBQ sauce over the top.
Garnish with chopped green onions and lemon wedges, if desired.
