- 6 cups cubed seeded watermelon
- 1/2 red onion, cut into thin half-moon slices
- 1/3 cup apple cider vinegar
- 2 tablespoons chopped fresh mint, or more to taste
- 1/2 teaspoon ground black pepper
- Toss watermelon, red onion, apple cider vinegar, mint, and black pepper together in a large mixing bowl. Refrigerate until chilled completely, about 1 hour.