Sand bags are good but soon rot … i prefer this method
or start with EMPTY Gabion’s , ones of the right dimensions, — preferably a thinner type like 1 a foot thick or less – they are made in many sizes — 3 foot by 4 foot by 1/2 a foot and use them as you would bricks .. tying them together with wire, obviously with the 1/2 foot being the width of the wall.
kinda like this (please excuse mspaint art)
Then attach the chicken wire to the outside of the wall and what will form the inside and plaster .
Plaster with a very fine plaster mix on the chicken wire — let it set and re-plaster until its quite thick .. maybe 1 inch