Chop all the vegetables, setting aside a cup each of watermelon and tomato as well as a half cup of cucumber.
Place 3 cups of watermelon, 3 cups of tomatoes, 1 cup of cucumber, garlic, shallot, basil leaves, salt, pepper, olive oil and jalapeno in the blender and mix until completely pureed.
Chill soup for at least 6 hours or until cold, easiest to do it the day before and refrigerate overnight or in the morning so it's cold for an evening meal.
Pour the soup in to bowls and place the reserved mixture of tomatoes, watermelon and cucumber in the center.
Top the vegetable mound with a tablespoon of feta cheese, basil, jalapeno and avocado, if using. Lightly drizzle olive oil over the top.