Soak the mussels in salted water for two hours. Then scrub each mussels shell with stiff brush or steel wood to clean thoroughly. Open the mussels with the point of a knife. Cut off the piece of hair in the inside and wash well in fresh water. Saute the onions in the oil until light brown, then add all the rest of the ingredients. Mix well. Now pick up a mussels, loosen the joint slightly so that when you close the shells they stay closed. Put a teaspoonful of the rice mixture in the shell, not too full, to leave room for the rice to swell, close the shells and arrange in the pan side by side and on top of each other, cover with a plate, add two cups of water, put the lid on and cook on slow fire for 1 1/2 hours or bake in the oven.