Preheat oven to 350°. Prepare a baking sheet with 1 – 2 TBSP of olive oil. Rinse fillets, pat dry. Juice lemon or lime over each fillet. In a food processor, crush walnuts. Place fillets (“skin” side down) on prepared baking sheet. Press crushed nuts on top of fish. Sprinkle with fresh ground pepper and salt. Bake for 15 minutes or until nut topping is slightly browned. Fish should flake when pierced.