Wrap the silken tofu in a paper towel. Put a weighted object (like a small saucepan) on the silken tofu to press out excess water. Once drained, cut into bite-sized cubes. Put tofu cubes in fridge uncovered for 20 minutes to remove excess moisture. Remove from fridge 10 minutes before cooking.
Season the minced pork for about 20 minutes
Mince the garlic. Chop the scallion. Chop the preserved mustard stems. Set aside for use.
Put stove to medium high heat and add some vegetable cooking oil into a frying pan. When the oil is hot, add the ground pork and let it sit in the oil to brown for approximately 2 minutes. Flip over to cook evenly.
Add the garlic and stir for 1 minute until the garlic is fragrant. Add preserved mustard stems and stir for 1 minute. Add chili garlic sauce and stir to combine.
Add oyster sauce and dark soy sauce and stir to coat.
Add cubed tofu and gently toss to incorporate. Be careful not to crush the tofu. Add water and let everything cook for 3-5 minutes at medium heat.
Add the scallions, stir, and remove frying pan from heat.