Dry Salmon fillet with paper towel. Salt each side of salmon generously. Place in fridge for 12-18 hours.
Rinse salmon under cold water; let it sit for few minutes in water.
Slice sideways (you get larger slice), very thin pieces. I tried to do it as thin as possible.
Place salmon in a dish, cover with oil and diced onions. Let all ingredients sit for at least an hour before serving.