Preheat oven to 375 degrees. Bake coconut flakes in a single layer on a rimmed baking sheet until toasted, about 3 minutes.
Divide half the sorbet among 6 tall glasses using a 2 1/4-inch ice cream scoop. Top each with a layer of watermelon, another scoop of sorbet, and then more watermelon. Sprinkle with lime zest and toasted coconut.