Bring a pot of well salted water to a bare simmer. Slide the tofu cubes in and let them sit for 3 minutes, then drain gently. This seasons the tofu and firms it up so it holds together in the sauce.
Heat the oil in a wok or wide pan over high heat. Add the pork and press it flat. Leave it for a minute before breaking it up, then keep frying until the edges brown and crisp, about 4 minutes. Lean pork has no fat to render, so the browning does all the flavor work.
Turn the heat to medium. Add the doubanjiang, black beans, garlic, and ginger. Fry for about a minute, stirring, until the oil stains red and it smells sharp and savory.
Pour in the stock, soy sauce, and sugar. Bring to a simmer.
Slide the tofu in. Simmer for 5 minutes, pushing the cubes around gently with the back of a spoon. Do not stir like you would a stir fry or the tofu breaks up.
Restir the cornstarch slurry and pour it in. Simmer 1 more minute until the sauce turns glossy and clings to the tofu.
Dust with the ground Sichuan peppercorn, scatter the scallions over, and serve with rice.