For the pancakes: In a large bowl, mix the flour with the salt and the Szechuan peppercorns. Add the scallions. Add the boiling water slowly and begin stirring it in immediately. Knead the warm dough until it's smooth. Place the dough ball in a lightly oiled bowl. Cover with plastic wrap and let rest for at least 2 hours at room temperature.
Turn the rested dough out onto a floured surface and divide into 8 equal parts. With a lightly floured rolling pin, roll each piece out until it's 1/4-inch thick. Use a cookie cutter to cut out 5-inch circles of dough (or just cut them out using a knife). Cover the prepared pancakes with a damp towel to keep them from drying out while making the rest. For best results, layer the pancakes on pieces of parchment paper to keep them from sticking.
Heat a little vegetable oil in a heavy frying pan over low heat. Add the pancakes and cook until browned on both sides (about 2 minutes altogether; the second side will cook more quickly than the first side). Continue with the remainder of the pancakes, placing the cooked ones on a tray lined with paper towels to absorb some of the oil.
For the garnish: To crisp up the duck skin, saute in a pan over medium heat until crispy, about 2 minutes (do not add oil). Once cooked, place the skin on a paper towel to absorb excess oil.
Top the pancakes with the shredded duck meat, crispy duck skin, scallions, cucumbers and hoisin sauce.