How to Grill Watermelon. Easy grilled watermelon is one of the most refreshing and healthy recipes you can make for desserts in the summer. This is a simple way to get some more flavor out of your grill, perfect if you're looking for ideas for food for side dishes for a bbq or backyard parties for a crowd. One of the most fun sweet treats for memorial day or the fourth of july too! You'll need watermelon, lime, salt, red pepper flakes, and sugar.