Place the cubed watermelon in a large mixing bowl and chill in the refrigerator for at least 10 minutes to enhance freshness.
Add the watermelon cubes, chopped cucumber, red bell pepper, mint leaves, vinegar, and olive oil into a blender.
4 cups watermelon flesh, cubed
Blend on high speed until the mixture is completely smooth and silky, about 30-45 seconds. The consistency should be uniform and free of chunks.
Taste the soup and season with salt and pepper, then blend again briefly to incorporate the seasonings.
4 cups watermelon flesh, cubed
Transfer the soup to a serving bowl and chill in the refrigerator for at least 30 minutes to allow flavors to meld and ensure the soup is well chilled before serving.
Serve cold, garnished with additional mint leaves or diced vegetables if desired, for a vibrant presentation.