Peel the onion, wipe the mushrooms with a damp cloth.
Separate the legs and chop them finely. Chop greens and onions finely. Boil the champignon caps in salted boiling water for 7-10 minutes, remove and put on a plate with the cap up, so that excess water flows out.
Fry the onions in oil, add the chopped mushrooms and fry, stirring occasionally, for 5 minutes. Add crackers and fry for 2 minutes. Add sour cream, salt, pepper, season to taste. Add greens and mix well.
Stuff the mushroom caps with the prepared mixture, put on a baking sheet (you can cover it with foil), sprinkle with cheese on top. Pour 100-150 ml of water, in which the mushrooms were cooked, onto a baking sheet (then the mushrooms will not be dry). Put the baking sheet in the oven, preheated to 180-190 degrees, and bake the stuffed mushrooms in the oven for 30 minutes.