Heat a cast-iron skillet over medium-high heat until hot.
In a shallow dish, combine the paprika, thyme, onion powder, garlic powder, salt, and red pepper.
Pour the melted butter in another shallow dish.
Dip the fish fillets in the melted butter, then coat with the seasoning mixture. Cook the prepared fish, in batches if necessary, until the fish flakes easily with a fork, 3 to 4 minutes per side. Spread the Cilantro-Lime Mayonnaise evenly over the toasted buns. Place the blackened fish on the bottom half of the bun, top with Mango Salsa, and cover with the top half of the bun.
In a small bowl, combine all the ingredients. Cover and chill.
Combine all the ingredients in a small bowl, tossing gently to coat. Cover and refrigerate.