Place fish in a large zipper-topped plastic bag.
In a small bowl, combine 2 tablespoons of olive oil along with remaining ingredients (lemon juice and zest through black pepper); pour mixture over Mahi Mahi fillets then seal bag and turn to coat well.
Refrigerate for at least 30 minutes or up to 6 hours.
At time of cooking, heat remaining 1 tablespoon of olive oil in a large skillet over medium-high heat.
Add Mahi Mahi steaks and cook for 4 minutes per side or until fish flakes easily when tested with a fork.
Serve hot or at room temperature.