Heat oil in a pot on medium heat. Add the pork belly and let sear for a bit, stirring occasionally. Then add the onion and kimchi, stir for 2~3 min.
Add water to the pot and then turn to high heat, then add the hon dashi. Stir it in so it's mixed well, bring to a boil then turn the heat down to medium high. Add the mushrooms.
Add the fish sauce, soy sauce, salt, white pepper, chicken bouillon. Taste it and see if you want to adjust, if it's very salty you could add a bit of sugar to balance it out.
Cut the tofu (into blocks or rounds depending on the packaging, if you're using very soft tofu be careful when transferring to pot or you can just break it up and scramble, it's your life!) Let simmer for 5~10 minutes. If you want to you can turn the heat down to medium low and put the lid on.
Mix in your veggies and taste again to see if you need to adjust anything. If your kimchi is not very spicy you can add some gochugaru (Korean hot pepper flakes).If you're using the egg, crack it into the center and let it simmer for 1 minute. Then kill the heat and sprinkle the green onions on top. Drizzle the sesame oil on top.
Enjoy! Serve with rice or whatever you prefer :)