Toss together in a serving bowl:
- 6 cups ½-inch pieces seeded watermelon
- ½ small red onion, diced
- 1 small jalapeño pepper, seeded and diced
- 3 tablespoons lime juice, or to taste
- 2 tablespoons chopped cilantro or parsley
- ½ teaspoon chili powder
- ½ teaspoon salt, or to taste
- ⅛ teaspoon cayenne pepper, or to taste
Serve at room temperature.