In a medium bowl, combine the diced cucumber, chopped onion and mint.
Whisk together the vinegar, 1-½ teaspoons of the olive oil and sugar in a separate cup or bowl. Season with salt and pepper.
Add dressing to the chopped vegetables, and mix well.
Heat grill to medium heat. Alternatively, preheat broiler.
Brush swordfish with remaining 1 teaspoon of olive oil; season with salt and pepper.
Grill (or broil) swordfish until opaque in the center, depending on thickness, about 4- 5 minutes per side.
To serve, place swordfish on individual plates and top with cucumber mint salsa.