Peel the grapefruit. Separate into segments and set aside.
Mix together the soy sauce and sugar and set aside.
Heat the coconut oil in a large fry pan. Sauté the ginger, garlic, onion and cayenne peppers until very fragrant. Add one tablespoon of the shredded coconut.
Push the spices to the outside of the pan. Add more coconut oil if the center of the pan is dry. Add the fish filets and sauté for 3 minutes per side in the middle of the pan. Be sure not to overcook the Mahi. Remove to a plate.
Add grapefruit to the pan and mix with the rest of the pan ingredients under low heat. Add the soy sauce and sugar. Adjust seasonings as needed.
Place a Mahi filet on each dinner plate. Drizzle the sauce on each filet and garnish with scallions and remaining shredded coconut. Serve with rice or a salad.