To make cucumbers and creme fraiche: In medium plastic container or flat-bottomed bowl, place cucumbers in single layer then sprinkle in some red onion and some salt. Repeat 4-5 times until all cucumbers and onions are layered. Cover and refrigerate 2-8 hours. Drain water from cucumbers and onions by pressing firmly (do not rinse). Add vinegar and toss to combine.
Just before serving, stir in dill and creme fraiche.
To make pan seared salmon: Debone and cut salmon into four pieces; season lightly with salt and pepper, to taste. In large saute pan, heat grapeseed oil and sear salmon. When slightly golden-brown, flip salmon and cook just long enough to sear other side. Remove from pan and place on platter with cucumbers and creme fraiche.