Blend watermelon cubes and lemon zest. Add 1 TB water, if necessary, to assist in blending until smooth.
If a sweeter flavor is desired add a few fresh strawberries to the mix before blending.
Optional step to prevent separating: pour half the mixture into ice cube trays until frozen, then add to blender and mix until you achieve a slushy consistency with no lumps.
Optional: For a fun flavor twist add the basil leaves to the blender as well. It creates a more adult flavor profile that is just as delicious!
Place clean popsicle mold on small tray or cookie sheet. Don't skip this step. Trust me, it prevents spills later!
Using a small funnel or liquid measuring cup with pour spout, fill each popsicle mold leaving ½" at the top for expansion.
Firmly attach lid to the top of mold and add popsicle sticks into each slot making sure they are straight. Do not push sticks all the way down - leave a good 1½" at the bottom for an adequate handle.
Carry the tray to the freezer and carefully lift the popsicle mold onto a level shelf and let chill for 3 hours until frozen.
Once frozen, run the bottom of mold under water for a few seconds and gently remove popsicles from each mold. Serve immediately or store flat in ziplock freezer bags in the freezer.