Heat a small soup pot over medium heat and add the oil. When the oil is heated, add the onion, stirring a few times before adding the meat. Stir and cook, then add the carrots and potatoes. Stir to combine well with the meat.
Add the water and bring it to a boil. Add the soy sauce, sake, mirin, and sugar. Lower the heat, cover the pot, and simmer until the carrots and potatoes are cooked through and the sauce has reduced.
Add the Shirataki noodles and cook for 1 minute. Add salt and the scallions. Turn off the heat and serve immediately.