Preheat the oven to 350F. Spread the pistachios on a small baking sheet and bake for 8-10 minutes, or until they smell toasty. When cool, coarsely chop the pistachios and set aside. (Tip: Place them in small zip-close bag and gently bash with a rolling pin until they are in pieces, but not pulverized.)
Season the salmon fillets with salt and pepper. Melt the ghee in a nonstick skillet over medium-high heat. When the ghee is hot, add the salmon pieces to the skillet with the skinless sides down. Cook for 2 minutes without moving, or until a golden crust forms and the fish easily releases from the skillet when you peek with a spatula. Turn the fish over and cook for an additional 3-5 minutes, or until the salmon is cooked through. A thermometer inserted into the thickest part of the salmon should register at 120-125F. The exact time will vary according to the thickness of the fillets. Transfer the salmon to a platter and let rest for 5 minutes, during which time the salmon will continue to cook.
Transfer the fillets to 4 plates. Immediately spoon ½ teaspoon of ghee on top of each fillet to melt, and use 4 of the lemon wedges to sprinkle each fillet with lemon juice. Sprinkle with the crumbled feta, pistachios and parsley and serve with remaining lemon wedges.
