1. Prepare the watermelon:
Cut the watermelon into chunks, removing any seeds if needed.

2. Blend the ingredients:
In a blender, combine the watermelon, Greek yogurt (if using), coconut water (or regular water), and honey or agave syrup. Add ice cubes if you prefer a colder, thicker smoothie.

3. Blend until smooth:
Blend everything together on high speed until smooth and creamy. If the smoothie is too thick, you can add a little more coconut water or regular water to reach your desired consistency.

4. Taste and adjust sweetness:
Taste the smoothie and add more honey or agave syrup if needed, depending on how sweet your watermelon is.

5. Serve:
Pour the smoothie into glasses and garnish with fresh mint leaves, if desired.