Place half of watermelon, cucumber, and all of the onion, cilantro and zest and juice of the lime in food processor and process until very smooth. Pour into serving bowl. Place remaining ingredients into food processor and pulse until very small pieces. Add to serving bowl. Stir in half of the feta. At this point, taste and add salt, pepper or sugar as desired. To serve, ladle into serving bowl and then sprinkle with remaining feta as a garnish.