Bring the water to a boil in a small saucepan. Stir in the bulgur and salt. Return to a boil, then lower the heat to a low simmer and cover. Cook for 15 minutes, until all the water is absorbed. Remove from the heat.
Meanwhile, cover the potatoes with salted water and bring to a boil in a large saucepan. Cook for about 10 minutes, until tender. Drain, reserving the potato water as well as the potatoes.
Heat the oil in a large cast-iron skillet and stir in the onion and garlic. Saute over medium heat for 7 minutes, then stir in the cooked bulgur and potatoes. Stir the soy sauce into ½ cup of the reserved potato water and pour it over the hash. Cook another minute, then serve at once.