In a small bowl, whisk together the olive oil, lime juice, and salt.

Heat up the grill on high, with the cover closed, until the grate is searing hot – about 10 minutes. Oil the grate by pouring a little olive oil on a triple layer of paper towels. Quickly rub the paper towels on the grates where you plan to sear the watermelon.

Generously brush the watermelon with the lime mixture on one side only. Arrange the melon wedges, basted side facing down on the grate. Baste the top of the wedges with the lime mixture. Grill 2 minutes per side.

Arrange on a serving plate, drizzle them with the remaining lime mixture, and sprinkle with the mint.