
Toast the pistachios. Set a small nonstick pan over medium heat. Add the pistachios and toast for 2 to 3 minutes, stirring with a wooden spoon, until fragrant.
Make the honey-lime syrup. Add the honey and brown sugar and warm, stirring constantly, for about 1 minute, or until the brown sugar fully dissolves. Turn the heat off and stir in the lime zest and juice. Set aside to cool for 5 minutes. Taste and, if needed, stir in more honey.
Finish and serve. Combine the watermelon and cantaloupe in a large, shallow serving bowl. Spoon the pistachio and honey syrup all over and serve.