Brush the grouper fillets with olive oil on both sides.
In a bowl, mix the paprika, onion powder, garlic powder, thyme, oregano, black pepper, cayenne pepper, and salt.
Coat each fillet thoroughly with the spice mixture, pressing it in to adhere.
In a separate bowl, combine the diced mango, red bell pepper, red onion, jalapeño, cilantro, lime juice, salt, and pepper. Mix well and set aside.
Preheat a cast-iron griddle over high heat until it is smoking hot.
Place butter on the griddle it will brown quickly. Then place fillets in the griddle and cook for 3-4 minutes on each side until the fish is blackened and flakes easily with a fork.
Serve the blackened grouper topped with the fresh mango salsa.