For the Lemon Allspice Syrup

1. Combine sugar, water, lemon zest, allspice, and red pepper flakes in a small saucepan.
2. Cook over medium-high heat until sugar dissolves, stirring occasionally.
3. Reduce heat to medium and cook until reduced by half (about 30 minutes), stirring occasionally.
4. Remove from heat and let cool for 10 minutes.
5. Strain the syrup and set aside.

For the Lemon Allspice Dressing

1. In a small bowl, whisk together 1/2 cup of the allspice syrup, vinegar, lemon juice, and salt.
2. In a large bowl, combine watermelon and peaches.
3. Pour the dressing over the watermelon and peaches and toss to coat.
4. Chill the fruit salad for up to 12 hours.

To Assemble the Salad

1. Toss the watermelon and peaches with the dressing.
2. Transfer the fruit to a serving platter.
3. Top with feta cheese and pistachios.
4. Garnish with 1 teaspoon of grated lemon zest.
5. Serve.