Preheat the oven to 400°F.
While the oven is heating up, place the whole but shelled pistachios in a plastic bag. Using a heavy sauce pot, rolling pin or meat flattener, smash the pistachios into tiny pieces. You’re looking for a bread crumb size. You could also use a food processor and pulse them into smaller pieces being careful not to process them into dust.
Transfer the pistachios to a round baking tin, pie dish or plate.
Rinse and pat dry the trout fillets with paper towels. Lightly oil the fillets on both sides, then season with salt and pepper.
Coat the flesh of the trout fillets with the pistachio pieces and transfer to a roasting pan, skin side down. Top the trout fillets with slices of lemon.
Place the fish into the oven and roast for 10 minutes or until the fish is done.
When the fish is done, remove it from the oven, plate your sides and transfer the fish fillets to the plate.
Serve and enjoy!