Preheat oven to 450 degrees.
Boil a large pot with water and cook the spinach for 30 seconds. Drain the water and immediately rinse the spinach with cold water. Try to remove as much liquid as possible after by squeezing the spinach.
Mix the spinach with all the other ingredients in a bowl, except for the oil and salmon. Put on the side.
Line a baking sheet with parchment paper and put some EVOO lathered on the paper.
Form a pocket on the side of each fillet by cutting a slice into the thickest part of each fillet. Evenly divide the spinach stuffing between the fillets and stuff generously.
Put the fillets on the baking pan with the skin side down and lather more olive oil onto the top of each fillet. Bake for 17 minutes, best served right out of the oven.