Put a skillet on at medium high and add just enough olive oil to coat the bottom. Put the the salt in a small bowl and the lemon juice. Whisk it up until the salt is dissolved. Add the oregano and mix it in. Very slowly trickle in the olive oil while whisking to blend it in with the lemon juice. Add the pepper and stir it up some more.

Cut up the onions and rinse and trim the asparagus stalks. Put them the skillet and stir them up once as they cook.

When they have softened up a little push them off to the side and put in the cod fillets. (or whatever kind of fish that your using) in the center of the skillet and cook for about one and a half  or two minutes a side depending on the thickness. They should be cooked only  to the point that they want to flake but are not browned.

Put everything on the serving plates. Whisk up the salmoriglio mixture and drizzle it over the fish and a little on the asparagus works real good too.