Preheat oven to 450 degrees F. Line baking sheet with non stick foil or spray foil with olive oil.
Rinse fish with water and then pat dry. Lay on baking sheet and bake for 8 minutes.
Remove from oven and brush melted butter on the top. Sprinkle with some salt and pepper. Return to the oven for another 8 minutes or until it is as done as you'd like in the thickest portion.
Mix together the lemon juice and mustard in a dish, brush on the top with a sprinkle of parsley when served. Serve with a lemon wedge if desired.