Wash, peel and finely chop the vegetables.
Potatoes, as usual for making mashed potatoes.
Cut the onion into medium cubes.
Mushrooms, if they are large, cut in half and put on a plate.
Fry the onion, add the mushrooms. Lightly fry.
Add the green onion, pre-chopped, and garlic powder. Simmer for a couple of minutes, remove from heat.
Boil the potatoes, drain the water and dry for a minute on low heat. Mash into a puree.