Cut the tofu in half the long way, and then into thirds the short way, to create 6 equal sized cubes of tofu from each 14oz brick, giving you 12 tofu cubes total.
Some of the edges of the tofu are more firm than others, so find a softer edge and cut a square into it with a pairing knife. Use a small spoon or melon baller to scoop out the insides of the tofu cube, being careful not the break any of the fragile sides or bottom.
Line up all the tofu cubes next to each other. Fill a mesh strainer with the cornstarch and tap it to dust the tofu evenly with cornstarch. This step will help the sausage stay firmly stuck inside the tofu.
Press some sausage into each tofu cavity. Push it in tight but again be careful not to fracture the tofu walls.
Preheat a nonstick pan over high heat with some oil. Add the tofu cubes sausage side down. Cook about 3-5 minutes on that side to fully brown. Flip them all to the next side and continue to cook, flipping every 3-5 minutes, until all 6 sides of each cube are lightly golden.
As they cook, mix together the sauce ingredients in a small bowl.
Line up the cooked tofu on a plate. Drizzle with the sauce. Top with the parsley and pickled onion. Serve.