In a small bowl mix together the spices and set aside.
Place a frying pan or cast iron skillet over high heat until it starts to smoke. Keep kitchen area well ventilated.
Toss the mahi mahi in melted butter and then coat with spice mixture on both sides. Press spice mixture to adhere.
Immediately sear on high heat 2-3 minutes per each side or until desired doneness is reached and center is cooked. Don't overcook as it will dry out. Serve immediately with slices of lemon and steamed rice.
Notes
Other ways to cook Mahi Mahi - A quick grilling works 4 minutes per side as does popping it in a 375°F oven for 8 minutes.