How to Make It
In a microwave-safe bowl, combine the vinegar with the 1/4 cup of sugar and 1 1/2 teaspoons of salt; microwave at high power until the sugar is dissolved, about 1 minute. Add the jalapeños and shallot and let stand at room temperature for 1 hour. Drain and pat dry.
Meanwhile, heat a cast-iron skillet until very hot. Blot the watermelon dry with paper towels. Sprinkle one side only with a thin layer of sugar. Add the watermelon to the skillet, sugared side down, and cook over high heat just until the sugar is lightly caramelized, about 30 seconds. Transfer the watermelon to plates with a spatula, browned side up, and let cool slightly.
In a medium bowl, toss the arugula and sorrel with the olive oil and season with salt and pepper. Mound the greens on the watermelon and garnish with the pickled jalapeños and shallot and the scallion. Dollop the crème fraîche on top. Arrange the peaches and Gorgonzola on the plates and drizzle the honey all over. Serve right away.
If sorrel is hard to find, double the arugula and toss with 1 tablespoon of lemon juice.