In a large skillet combine the water, soy sauce, ginger, raisins, and onion. Cover and bring to simmering over medium-high heat; simmer for 5 to 6 minutes or until raisins are plump and onion is tender. Remove raisins and onion with a slotted spoon. Transfer raisins and onion to a small bowl; stir in pepper. Set aside.
Add sliced pork to cooking liquid in pan. Simmer, uncovered, for 7 to 8 minutes or until pork is cooked through (just a trace of pink remains), turning once. Remove with a slotted spoon.
Serve pork in buns with cucumber slices, raisins, and onion.