In a large food processor or blender, blend the watermelon until smooth. Alternatively, if your food processor or blender isn’t large enough, you can work in batches.
Then, add the diced tomatoes, cucumber, white onion and ginger and purée until well blended. Finally, add the balsamic vinegar, olive oil and salt and pepper to the mixture, and pulse once again for a couple of seconds to combine. Add a taste and adjust the seasonings, adding a bit more salt and pepper if necessary.
Pour the soup into a large bowl.
Cover, and refrigerate for a couple of hours before serving.
In the meantime, mix all the ingredients for the garnish.
To serve, pour the soup into chilled bowls or glasses and scatter 2 to 3 tablespoons of the corn and onion mixture on top.