Wash the bean sprouts thoroughly and prepare them.
Finely chop the onion and green onion.
Pour water into a pot and bring to a boil.
Once the water boils, add the bean sprouts, onion, and green onion, and boil for 2-3 minutes.
Add the oatmeal and boil for another 2-3 minutes.
Season with soy sauce for soup, minced garlic, salt, and pepper.
Serve in a bowl and, if desired, sprinkle with seaweed flakes or chili powder.