Preheat oven to 400ยบ F and lightly spray a sheet pan with cooking oil.
In a small bowl, add the Hellmann's Mayonnaise, lemon zest , parsley and black pepper and mix to combine.
Pat each fish fillet with paper towels to dry and place on the prepared sheet pan.
Divide the mayonnaise mixture and spread atop each fish fillet.
Top with the chopped pistachios, pressing lightly to help adhere to the fish.
Bake for 15 - 20 minutes, until the fish flakes with a fork. (Bake time can vary based on the thickness of the fillet.)