Heat the oil in a large skillet over medium heat. Add the pork and cook, stirring and breaking up the meat into bite-size chunks, until just pink, about 8 minutes. Add the ginger and garlic and continue to cook until the pork is light brown, 5–8 minutes. Add the stock, chili garlic sauce, vinegar, soy, tahini, sugar, and Szechuan peppercorns. Cook until thickened, 7–10 minutes. Stir in the peanut butter.
Meanwhile, brush the buns with chili oil and toast them.
Spoon the pork between the toasted buns. Sprinkle with the scallions and peanuts and serve with cucumber salad.
For the Cucumber Salad: In a medium bowl, whisk together the vinegar, chili oil, sesame oil, sugar, and salt until the sugar dissolves.
Halve the cucumbers lengthwise and scoop out the seeds if they are seedy. Place the cucumbers cut side down on a cutting board and lightly smash them with a cleaver or chef’s knife until they crack in a few places. Slice into ¾-inch half-moons.
Toss the cucumbers in the dressing and top with the sesame seeds, peanuts, and cilantro.
