Peel the onions and potatoes. Boil the potatoes in salted water, then drain almost all the water. Chop the onions and green onions. Slice the mushrooms.
In a frying pan with heated oil, fry the mushrooms until the moisture evaporates, then add the onions and fry everything together for 4 minutes. Remove from heat, add green onions and stir.
Puree the boiled potatoes along with a small amount of the water in which they were boiled, add the egg, salt and pepper and mix well.
Form the mashed potatoes into a tortilla, put the filling in it and cover with another tortilla. Make the rest of the pies in the same way.
Beat the egg in one bowl and place the breadcrumbs in another. Dip each patty in the egg, then roll in breadcrumbs and fry in a frying pan with heated oil until golden brown (about 5 minutes on each side).