Step 1

Slice and juice the lemon. Cut half the lemon into thin slices. Juice the remaining half, you should have about 1 1/2 tablespoons of juice; set both aside.

Step 2

Season the mahi mahi. Pat the mahi mahi dry with paper towels. Season all over with 1 teaspoon of the salt and a few grinds of pepper.

Step 3

Pan sear the mahi mahi. Heat the oil in a large cast iron skillet or nonstick frying pan over medium-high heat until just starting to smoke, 3 to 5 minutes. Add the mahi mahi and sear undisturbed until well browned on the bottom and the sides are cooked just past halfway up the fillets, about 4 minutes. Flip the fillets and continue to sear until just cooked through and the flesh flakes easily, 2 to 4 minutes more depending on the thickness of the fillets. Transfer to a serving platter.

Step 4

Add the lemon juice and garlic over medium-low heat. Reduce the heat to medium-low. Add the lemon juice, garlic, and remaining 1/4 teaspoon salt. Scrape up any browned bits from the bottom of the pan with a wooden spoon.

Step 5

Add the lemon slices and butter. Add the lemon slices, then stir the butter in one piece at a time, waiting until each piece is almost melted before adding the next.

Step 6

Season the sauce. Remove the pan from the heat. Stir in the parsley. Taste the sauce and season with more salt and pepper and needed. Pour over the mahi mahi and serve immediately.