Pre-heat grill the medium heat to medium-high heat.
Brush both sides of the fillets with olive oil, and season with salt and pepper.
Place mahi-mahi on to the grill, and cook the first side for about 5 minutes. Once the fillets release from the grill, and are no longer sticking, they should be good to flip.
Flip the fillets, and cook the second side for about 5 more minutes. Once it reaches 140°F, it is ready. Remove it from the grill.
Season with lemon juice, and serve.
Recipe Notes
Depending on the thickness of your fillets, and the heat of your grill, the cooking times may vary. The fillet is done when it reaches 140°F, and it begins to flake when poked with a fork.