Combine creme fraiche, mayonnaise, salt and pepper, dill, capers, lemon juice, horseradish and red pepper flakes, if using. Set aside.
To cook greens:
In a large skillet, melt the butter over medium high heat.Stir in the napa cabbage, green onions, and garlic. Saute 5 minutes, then turn down heat to medium, add water or broth and cover. Cook about 5 more minutes, till desirerd tenderness. Keep warm and set aside.
To cook salmon:
Heat oil in large skillet over medium high heat(I use same pan greens were cooked in or cook in separate skillet while greens are cooking). When hot, add salmon, skin side up(if it has skin on it). Sear until well browned, about 4-6 minutes. Turn the salmon over and sear other side until just cooked through, about 3-5 more minutes.
Divide the cooked napa cabbage evenly on 4 serving plates. Spread out a little to make a "bed". Place salmon on top of greens. Spoon sauce over top of salmon. Garnish with a little parsley or fresh dill, if desired. Enjoy!