Partially freeze tri-tip until firm and slice thinly, across the grain. Combine soy sauce, chili paste, garlic, sugar, sesame oil, onion and vinegar. Using 3/4 mixture, marinade beef for 3 hours and reserve ¼ mixture for finishing. Quickly grill beef over high heat, turning after meat begins to brown. Toss with reserved marinade and place on warmed tortillas. Top with shredded cabbage, a pinch of cilantro, green onion, sesame seeds, gochujang, kimchi and Sour Cream Sauce (recipe follows). Serve with lime wedges, more kimchi and Sriracha hot sauce.
Sour Cream Sauce
Combine all ingredients and adjust to taste.
* Other cuts of meat may be substituted. Flanks sirloin or chuck roast will also work well.