Boil 1 cup of water and 4 teaspoons of soy sauce in a small saucepan.
Peel and cut two potatoes into halves lengthwise. Lay the potato halves down on the flat side and chop them lengthwise into approximately 1/8" thick slices. Basically, half moon potatoes.
Once the soy sauce/water mixture boils, throw in the potatoes. Let it simmer and cook with the lid on for about 10-15 minutes.
The level of saltiness of the soy sauce varies from brand to brand, so you might want to start with 3 teaspoons of soy sauce and add more at the end if necessary.
Feel free to add other veggies, like carrots, onions or even beans!