I use my salad spinner to give spinach a bath: place the spinach inside the sieved inside part and then fill the entire thing with cold water. Lift the inside part of the spinner out, then drain the water. Repeat until the water is completely free of silt. Then spin the spinach dry.
Prepare 12 oz. udon or other noodles according to directions, but drain and rinse before while they are still a little firm.
Clean and rinse 1 large or 2 small leeks. Cut into julienne strips, lengthwise, about 2″ long.
Rinse 6 oz. of mushrooms and slice.
Cut the stems off 1 bunch of spinach, then soak the spinach in water and lift out to drain. Repeat until there is no silt in the water. Spin dry the leaves.
In a small saucepan, combine 1/4 C. soy sauce, 2 T. fresh squeezed orange juice, 1 T. lemon juice, and 1 T. sesame oil. Simmer for 5 minutes.
In a wok or large skillet, heat 2 T. safflower or peanut oil and add the leeks. Saute over medium heat, stirring frequently, until they are wilted. Add the mushrooms and cook another 5 minutes.
Raise the heat to high and add the noodles. Stir fry until they start to brown and/or stick to the pan. Make a circle in the center and add the sauce. As soon as it boils (which will be quickly), stir together with the noodles and add the spinach. Cook for just a minute or two, until the spinach is completely wilted.
Season with salt and pepper.