I know the picture isn't great but I started drinking it and couldn't stop.
2 cups frozen cubed watermelon
1 ripe banana
lime juice from 2 limes (it has a strong lime flavor so cut back if you don't like that)
lime zest from 1/2 a lime
1/2 cup Sprite (or more to make is smoother)
Blend all together. Easy Peasy.