Bring a pot of salted water to a boil, gently add the tofu cubes, and simmer for 2 minutes; drain carefully and set aside.

Heat the vegetable oil in a wok or large skillet over medium-high heat until shimmering.

Add the ground beef and stir-fry until crispy and browned, breaking it up into small pieces with a spatula, about 3-4 minutes.

Reduce heat to medium, then add the Doubanjiang, fermented black beans, minced ginger, and minced garlic.

Stir-fry the aromatics for about 1 minute until the oil turns red and the mixture is fragrant.

Pour in the chicken stock (or water), soy sauce, and sugar, stirring well to combine.

Gently slide the blanched tofu cubes into the sauce, taking care not to break them.

Simmer for 3-5 minutes, allowing the tofu to absorb the flavors of the sauce.

Stir the cornstarch slurry again and pour it slowly into the pan, gently shaking the pan or pushing the sauce with the back of a spoon to thicken.

Once the sauce clings to the tofu, sprinkle with the ground Sichuan peppercorns and chopped green onions.

Remove from heat immediately and serve hot over steamed white rice.