Combine mango, tomato, onion, lime juice, jalapeño, and cilantro. Add salt and pepper, then mix and set aside.
Gently pat mahi mahi dry with a paper towel to remove excess moisture. Set aside.
Combine spices in a shallow bowl. Coat both sides of the mahi mahi fillets with the blackening spices.
In a cast iron skillet, heat avocado oil over medium-high heat. Carefully add seasoned mahi mahi fillets and cook for 3-4 minutes per side or until fish flakes apart easily with a fork.
Serve mahi mahi with mango salsa over a bed of rice, if desired.
