Have a pot of boiling water on the stove. Place the buckwheat noodles into the boiling water and cook for about 4 minutes. Meanwhile, season the pork with the salt and ground peppercorns. Heat the oil in a saute pan and sear the pork tender on all sides for 8 minutes, making sure to get a nice crust on the outside. Remove and cool slightly. Drain the noodles, and add them to the hot chicken stock. Add the chili peppers, shiitakes, and mushroom soy sauce, continue to simmer. Thinly slice the pork tender and add it and the cilantro to the noodle broth. Season and ladle yourself out a big bowl.