Take a sheet tray and place the Mahi Mahi filets on it. Now brush olive oil on all sides of the filets and set aside.
Mix black pepper, paprika, onion powder, garlic powder, and kosher salt in a small bowl. Use this mixture to season the filets. Rub the seasoning well on the fish to allow the flavors to infuse. Allow to marinate for a few minutes.
Get your grill ready by preheating it and lightly oiling the grates over medium-high heat. When the grill is hot, place the Mahi Mahi filet flesh-side down. Cook for 3 to 5 minutes on each side till you get your desired doneness.
Take the fish off the grill and brush with melted butter. Garnish with chopped parsley and serve.