Thaw the Mahi Mahi if it's frozen, ideally overnight in the fridge. Alternatively, you can submerge it in cold water for a quick thaw.
Drain the thawed fish in a colander and place it between layers of paper towels to absorb excess moisture.
Zest the lemon and squeeze its juice. Chop the zest if it’s in large pieces for better distribution.
Combine the lemon zest, lemon juice, chopped capers, olive oil, garlic powder, onion powder, dried parsley, and black pepper in a bowl. Whisk together to create the marinade.
Place the fish filets in a Ziploc bag and pour the marinade over. Seal and let marinate in the fridge for one to two hours.
When ready to cook, drain the fish and let it come to room temperature.
Preheat the grill to high, spraying the grates with non-stick spray or brushing with oil.
Lower heat to medium-high and place the fish on the grill. Cook at an angle for 2 to 3 minutes until grill marks appear.
Rotate the fish to create crosshatches and cook for another 2 to 3 minutes on the same side.
Turn the fish over and grill for about 2 to 3 minutes or until it feels firm but not hard. Total cooking time should be around 9 minutes.
Serve hot, with additional lemon slices for squeezing on the table if desired.
