Marinate Meat: In a bowl, mix the soy sauce, sesame oil, brown sugar, garlic, ginger, and chili paste. Add flank steak to a gallon size resealable bag. Pour in marinade and press it around to coat all sides of the meat. Refrigerate for at least 1 hour, or up to overnight. Remove meat from fridge 30 minutes before cooking.

Kimchi Salsa: Mix all ingredients together. (Could be made a day or two ahead).

Cook Steak: Clean and grease your grill (or use a grill pan on the stove). Heat on high and once hot, remove steak from marinade and place on grill. Cook for 3-4 minutes, then flip to the other side and cook for 3-4 more minutes, to your desired doneness; 125 to 130°F for rare, 140°F for medium rare, and 150°F for medium.

Remove to a cutting board to rest for 5-10 minutes before slicing into very thin slices.

Assemble Tacos: Warm corn tortillas on a hot, dry grill for a few seconds on each side. Top tortillas with a few slices of steak, a good spoonful of kimchi salsa, a little bit of sour cream, and some cilantro on top.