Slice Napa cabbage and onions. Remove maitake mushrooms from the package and separate into small pieces by hand.
Heat a small pot over medium heat. Pour sesame oil and cook vegetables until soft. Reduce heat when necessary and avoid burning the vegetables.
In the same pot, pour in water and sprinkle dashi powder. Bring to boil.
Once boiled, turn off the heat and mix in miso paste. Turn on the heat again and cook for about 1-2 more minutes over low heat.
Serve in a bowl and enjoy with rice or fish!