DIRECTIONS
Season & rest the fish: On a large plate/platter, season the mahi mahi fillets with old bay seasoning- to taste, on all sides. Set the fish aside to rest and sit until they reach room temperature, about 20 minutes.
Prep the umami sauce: In a small bowl or measuring cup, combine the fish sauce, lemon juice, soy sauce, brown sugar, and garlic. Whisk the mixture together very well to thoroughly combine and set aside.
Sear the fish: Heat the oil in a large nonstick skillet over medium-high heat. Once the oil shimmers, gently swirl the skillet around to evenly coat the bottom. Add the mahi mahi fillets into the skillet. Cook the fish, undisturbed, until a golden-brown sear appears on the bottom and the sides are cooked about halfway up the fillets, about 3-4 minutes. Then use a fish spatula (or any similar utensil) to carefully flip the fillets onto the other side. Let the other side cook for 1-2 minutes or until the fish fillets are opaque in color (no longer translucent) and just cooked through with easily flaked flesh.
Add umami sauce + butter & simmer: Reduce the heat to medium-low. Pour the sauce into the skillet followed by the pieces of butter. Let the sauce and butter simmer until the butter melts through, about 1-2 minutes. Then sprinkle the parsley over the fillets and grab a spoon and baste the fillets with the sauce. Shut off the heat and remove the skillet from heat. Continue basting and gently swirling the skillet to move the fillets around in the sauce to meld, about 20 seconds of this with the residual heat.
Serve pan-seared mahi with umami butter sauce alongside your favorite side items (mashed potatoes, green beans, etc.) Enjoy!