Turn on the stove, set the pot atop and set the temperature to medium-high. Pour in water, soy sauce, mirin, chopped garlic and oyster sauce. Bring to boil.
Add the beef slices and let simmer for 4 – 5 minutes.
Toss chopped onions into the pot together with beef and the soy sauce mix, then allow to simmer for a few more minutes or until the onions become translucent.
Cook the rice according to directions.
Adjust taste to your liking by adding salt, pepper, and sugar.
Dissolve a portion of the cornstarch in 1/2 cup of water and add to the mix in order to have a thicker sauce. Add more if you need the sauce to be a bit thicker.
Put the rice in individual bowls (fill it to the top) and top it with the beef misono, then add the stir-fried bean sprouts mix as additional toppings.
Sprinkle with toasted sesame seeds and serve.