This is one of our favorite meals. I originally got the recipe from William Sanoma Grilling book, but have made many alterations.
2 ripe mangoes
1 or 2 limes for juice and some zest for decor
big, big bunch of cilantro
3 inches of chopped and also finely grated fresh ginger
1 hot pepper-like a jalapeno
1/2 red onion
Cube the mango, squeeze the lime juice, zest some lime, finely chop 2 inches of the ginger, grate one inch and use the juices, finely chop the jalapeno and red onion. Mix all together. Finely chop half the bunch of cilantro and tear off the leaves in small pieces of the other part. Mix all together. Taste it. Sometimes it can be lacking lime juice. Add a bit of salt. Place in fridge until needed. I usually serve it in a bowl on the side after I place one or two spoons of the salsa on the tuna. Serve tuna with a few side veggies.
Tuna, grill for 2-3 mins on each side. I like my tuna rare but here are a few suggestions on grilling tuna http://bbq.about.com/od/fishandseafood/a/aa103004a.htm