(Makes 2 servings, recipe slightly adapted from one which appeared in Weeknight Grilling, a magazine published by Cuisine at Home.)

2 pieces Mahi Mahi

Sauce/Marinade:
1/4 cup soy sauce
1 1/2 T Rice vinegar (not seasoned)
1 T sesame oil
2 T Splenda or brown sugar
1 green onion, thinly sliced
1 tsp. garlic puree (also called ground garlic)
pinch of cayenne pepper or a dash of hot sauce

Combine soy sauce, rice vinegar, sesame oil, Splenda or brown sugar, green onion, garlic puree and cayenne or hot sauce in small bowl. Put half of mixture into a small ziploc bag with the two pieces of fish and marinate at room temperature for 10-15 minutes.

While fish marinates, spray grill with non-stick spray or wipe with olive oil, then preheat grill to medium-high (you can only hold your hand there 2-3 seconds.)

Put fish on grill with top side down and grill 2-3 minutes (until you can start to see grill marks, I have to lift it up to see.) Rotate 45 degrees on same side and cook 2-3 minutes more to get criss-cross marks. Turn fish over and cook about 3-4 minutes more. Total cooking time will not be more than 8-10 minutes, The fish should feel barely firm when it’s done; don’t overcook. Serve hot, with dipping sauce on the side.

This recipe was used on Tuna in the magazine, and I think it would also be very good on Salmon.
http://kalynsprintablerecipes.blogspot.com/2009/09/soy-grilled-mahi-mahi-recipe-with.html