In a medium bowl, combine the diced mango, red onion, bell pepper, jalapeño, cilantro, lime juice, and salt. Toss thoroughly and refrigerate to allow flavors to meld.
Pat the salmon fillets dry with paper towels to ensure optimal spice adhesion and searing.
Brush both sides of each salmon fillet with melted butter.
Dredge the fillets in the blackened seasoning blend, ensuring an even and thick coating on all sides.
Heat a cast-iron skillet over high heat until it begins to smoke slightly.
Add the oil to the skillet, then carefully place the salmon fillets into the pan.
Sear the fillets for 3 to 4 minutes until a dark, blackened crust forms.
Flip the fillets carefully and cook for an additional 3 minutes or until the internal temperature reaches 145 degrees Fahrenheit.
Remove from the heat and serve immediately, topped with a generous portion of the chilled mango salsa.