Mix the mayonnaise, curry and relish together and spread evenly over the flatbread or tortilla. Sprinkle the rice evenly over the bread leaving a 1-inch wide strip down the length of a long side of the bread without rice and just the sauce exposed. Press down on the rice to pack. Place the salmon and watermelon in a compact line (on top of the rice) down the edge of the other long side of the bread - on the opposite side from the long side without the rice.

Starting with the side of the bread that has salmon, rice and watermelon, roll over the bread to enclose the salmon and seal the roll with the strip of bread with the sauce and no rice forming a cylinder. Wrap tightly in plastic wrap and refrigerate for 1 hour. Using a sharp, serrated knife cut the cylinder into 2-inch thick slices simulating the look of sushi. Arrange on a platter and serve.

Source:

Watermelon.org