Heat sesame oil in a pot or stove-top casserole dish. Add pork and fry for 2 to 3 minutes. Then add onion and stir fry for another minute.
Add garlic, gochujang, and napa cabbage kimchi. Continue to stir fry for 3 minutes.
Pour in kimchi juice and 1½ cups (360ml) water. Bring to a boil, reduce heat, cover, and allow it to simmer for 15 minutes.
Add sliced tofu and continue to cook for another 5 minutes.
Turn off heat. Add sliced green onions.
Serve immediately with steamed rice.