Make the pickled watermelon: Quarter the watermelon, then use a paring knife to remove most of the fruit, leaving about 1/4 inch of fruit on the rind. (Reserve the fruit for another use.) Trim the outside skin from the rind and discard. Cut the rind into 1/2-inch pieces; combine with the tomato and bell pepper in a bowl.
Combine 1 cup water, the vinegar, sugar, allspice, star anise and 4 teaspoons salt in a medium saucepan. Bring to a boil, stirring to dissolve the sugar, then pour over the watermelon rind mixture. Let cool to room temperature, then cover and refrigerate at least 4 hours and up to 1 week.
Make the salad: Bring a saucepan of salted water to a boil. Add the beans and cook until crisp-tender, about 5 minutes. Drain and transfer to a bowl of ice water to cool. Drain, pat dry and cut into 2-inch pieces.
Using a slotted spoon, transfer 4 cups of the pickled watermelon mixture to a large bowl. Add the beans, black-eyed peas, jalapeno and olive oil; season with salt and pepper and toss. Cover and refrigerate at least 1 hour before serving.