Heat a cleaned grill to high heat and season it with oil to ensure your fillet doesn't stick. You can do this by dipping a paper towel in cooking oil and wiping it over the grates to season them. Do this about 4-5 times.
Brush the fish with olive oil, then sprinkle with salt and pepper.
Grill each side for only 1.5 to 2 minutes. The center should be raw and lukewarm to the touch, or the tuna will be tough and dry.
Let the tuna rest for 5 to 10 minutes; serve with the cherry salsa.