Chop the onion, heat the vegetable oil in a frying pan and send the onion to fry.
Add coarsely chopped mushrooms, fry all together, stirring, for 5-7 minutes.
Remove from heat and allow to cool.
Cut the beets into small cubes.
Combine the chopped beets, pickled cucumbers, fried onions with mushrooms, green peas in a bowl (the liquid from the jar with peas is pre-drained).
Add the crushed garlic, season with salt and pepper mixture to taste.
Add finely chopped dill and green onions. Stir and bring to the table.