Step 1

Heat the grill to high. Heat an outdoor gas grill to high, or prepare a charcoal grill for high, direct heat grilling.

Step 2

Cut the watermelon. Trim the ends off the watermelon. Stand the watermelon on one cut end, cut in half, then cut each half in half again. Cut the quarters into 1/2-inch-thick slices.

Step 3

Season the watermelon. Combine the sugar, lime zest, and red pepper flakes in a small bowl. Sprinkle the watermelon slices on both sides with the sugar mixture, then rub the sugar mixture in to create an even coating.

Step 4

Grill the watermelon. When the grill is hot, add the watermelon slices in a single layer and grill until warmed through and grill marks appear, 2 to 3 minutes per side.

Step 5

Serve. Serve the grilled watermelon on its own with lime wedges, topped with feta cheese or Greek yogurt, or as dessert with a scoop of ice cream.