Preheat the oven to 350°. Lightly brush a nonstick baking sheet with olive oil. Heat the 3 tablespoons oil in a large skillet. Season the salmon with salt and pepper and press 1 side of the fillets into the chopped pistachios. Add 3 fillets to the skillet, pistachio sides down, and cook over high heat until lightly golden, about 2 minutes. Carefully transfer the salmon to the baking sheet, nut sides up, and repeat with the remaining 3 fillets. Bake for 6 to 8 minutes, or until the flesh flakes but is still slightly opaque in the center. Let rest on the baking sheet for 5 minutes before serving.