Prepare Beef and Kimchi: Heat sesame oil in a large pot over medium heat. Add sliced beef and cook until lightly browned.
Add Aromatics: Stir in garlic, ginger, and onions. Cook for 2–3 minutes until fragrant.
Add Kimchi and Seasonings: Add chopped kimchi, gochugaru, soy sauce, and sugar. Stir-fry for 3–4 minutes to bring out the kimchi’s flavors.
Simmer the Broth: Pour in broth (or water), bring to a boil, then reduce heat and simmer for 20 minutes.
Add Tofu and Vegetables: Add tofu, mushrooms, zucchini, or any additional vegetables. Simmer for another 10 minutes until tofu and vegetables are tender.
Adjust Seasoning: Taste the soup and adjust with salt, soy sauce, or gochugaru as needed.
Serve: Garnish with sliced green onions and serve hot with steamed rice.