Preheat the grill to medium-high.
Cut the melon in half, then cut the halves into 1-inch slices and place on a platter. In a medium bowl, whisk the lemon juice, olive oil, and honey. Brush the melon slices with the dressing. Reserve remaining dressing.
When the grill is hot, oil the grate. Grill melon slices until marked, about two to three minutes per side. Transfer to the platter.
When the melon is just cool enough to handle, cut off the rind and cube the flesh.
In a large bowl, place the watermelon, cucumber, red onions, and basil. Drizzle the remaining lemon dressing over the watermelon mixture, sprinkle with coarse salt, and toss to coat. Serve immediately.
QUICK TIP: Seed your cucumber in a snap: Cut it in half lengthwise, then press a spoon into the seed channel in the center and gently scoop out the seeds.
For more plant-based grilling recipes, see “Vegan Grill Recipes“.
Photos: Andrea D’Agosto; Prop Styling: Alicia Buszczak; Food Stylist: Paul Jackman