Add sesame oil to a large saute pan and heat to medium. Add onion and garlic and saute for 2 minutes.
Add ground beef and cook until browned, breaking up as it cooks. Saute for 7-8 minutes over medium until most of the pink is gone. Add vinegar, ketchup, tomato paste, and gochujang to the pan and stir well so that it is all mixed well and all of the beef is coated. Cook for another 2-3 and then finish with green onions.
Add a large helping of meat to each bun, top with kimchi and serve!
Notes
StorageFridge: The cooked beef is great to prepare in advance as it will keep in the fridge for 4-5 days. Freezer: You can make the beef and then store it in the freezer for up to 4 months. Take out of the freezer and let thaw overnight in the fridge before reheating.SubstitutionsGround Beef: We prefer a leaner ground beef for this recipe, at least 85%-90%, but you can of course use something lower, but then we would suggest draining the excess fat before adding the ketchup, gochujang, etc.Onion: White is our go-to, but you can of course use yellow. Seasoned Rice Vinegar: It's really best to use seasoned rice vinegar instead of unseasoned because of the added sweetness. You can also use mirin. Kimchi: Use your favorite! We usually use a less spicy kimchi for this (for our kids), but my husband also likes it with a spicy kimchi.