Combine kimchi, water, sugar, and garlic in a large skillet over medium-high heat. Bring to a boil. Stir in pork belly, luncheon meat, and kochujang. Add tofu and mushrooms; stir carefully so you don't break up the tofu. Reduce heat to medium-low. Cook until kimchi is softened and pork is slightly pink in the center, 20 to 30 minutes.
