In a large pot, heat sesame oil over medium heat. Add the sliced onion and garlic, sauté until fragrant.
Add the chopped kimchi and cook for a few minutes until it softens.
Pour in the chicken or vegetable broth and bring to a simmer.
Add the cubed tofu and canned tuna (with the water drained) to the pot. Stir gently to combine.
Season with soy sauce, gochujang (if using), salt, and pepper. Adjust seasoning to taste.
Let the stew simmer for about 10-15 minutes to allow the flavors to meld together.
Before serving, sprinkle chopped green onions on top.
Serve the Tuna Kimchi Stew hot over cooked rice.
Enjoy!