Rinse the mushrooms with running water and wipe them off with a napkin.
We gently break off the legs.
Cut the legs very finely and mix with beets and onions, cut into small cubes. Salt and pepper.
For the sauce, we pass the garlic through a press, add a couple of tablespoons of vegetable oil to it, mix everything well.
Put the champignon caps with the inside side up on a baking sheet covered with parchment and oiled with vegetable oil. Fill the champignons tightly with the filling. Using a teaspoon, spread the sauce evenly over the filling. We bake the stuffed mushrooms first on the upper level, preheated to 200 degrees, in the oven for about 10-12 minutes. When the filling begins to brown, reduce the temperature in the oven to 150 degrees, and put the baking sheet with mushrooms on the very bottom of the oven. The abundant release of juice from the mushrooms and the filling will begin, in which the stuffed mushrooms will reach readiness. We bake for another 15 minutes.
Sprinkle the prepared baked stuffed mushrooms with herbs.