Prepare the produce: Wash and chop all the fresh ingredients.
Blend it up: In a blender or food processor, combine the watermelon, cucumber, tomatoes, bell pepper, red onion, garlic, red wine vinegar (or lime juice), and olive oil. Blend until smooth.
Season to taste: Add salt and pepper to your preference. For extra flavor, toss in a few fresh basil or mint leaves and pulse again.
Chill: Transfer the gazpacho to a bowl, cover, and chill in the refrigerator for at least 1 hour for the best flavor.
Serve and garnish: Pour into bowls or glasses. Top with feta, diced cucumber, or fresh mint if desired. Serve cold.