Watermelon Sandwich With Feta, Olives, and Fresh Herbs

Ingredients

• 4 thick slices seedless watermelon (1/2-inch thick, rind removed)
• 1/2 small red onion, thinly sliced
• 1 small handful fresh mint leaves
• 1 small handful fresh basil leaves
• 1/2 cup feta cheese, crumbled
• 1/4 cup pitted Kalamata olives, sliced
• 2 teaspoons extra-virgin olive oil
• Freshly ground black pepper, to taste
• 2 ciabatta rolls or similar crusty sandwich rolls, sliced in half