Heat oil in a large pot over medium-high heat. Sear the beef until browned on all sides, then remove and set aside.
Add kimchi, garlic, and ginger to the pot. Stir and cook for 3 minutes until fragrant.
Stir in gochujang, gochugaru, soy sauce, and fish sauce. Mix well to coat the kimchi.
Pour in beef broth and return the beef to the pot. Bring to a boil, then lower the heat and let simmer for 60–90 minutes.
Add mushrooms and tofu in the last 15 minutes of cooking.
Garnish with scallions and drizzle with sesame oil before serving.