Combine the sliced dried tomatoes with the water. Set aside.
If using Hokto Kinoko's brand of white beech mushrooms, trim the base as the package describes.
Prepare the string beans by snipping off the ends, then cutting into halves or thirds.
Heat the oil in a large non-stick skillet over medium-high heat. Add a bit of mushroom. When it begins to sizzle add the rest of the mushrooms, separating them as you go along. Add the salt and red pepper flakes. Cook, stirring often, for about 5 minutes or until the mushrooms sweat and brown a little.
Add the green beans, rehydrated tomato slices, and the soaking water to the pan and stir. Cover the pan and steam until the beans turn a bright green and become tender with a crunch.