Stop at a Korean market on the way home from work, and you can have this soothing, vibrant dish on the table in 30 minutes. Slideshow: More Tofu Recipes
In a medium-size nonreactive pot, cook the pork belly pieces over moderate heat, stirring occasionally, until the fat is sizzling and the pork is light golden, about 8 minutes. Add the kimchi and the onion, and cook, stirring occasionally, until the onion is softened, about 5 minutes.
Add the reserved kimchi liquid, mushrooms, gochujang, gochugaru, and 4 cups of water, and bring to a boil. Reduce to a simmer, and cook over moderately low heat for 10 minutes.
Season the stew with salt. Stir in the tofu, breaking it up slightly with the spoon, and bring to a boil; remove from the heat. Serve the stew hot with steamed rice.