Remove the seeds from the watermelon chunks if present. Use a knife and cutting board to cut the watermelon into evenly sized cubes for easy blending.
Place the watermelon chunks into a blender. Add the lemon juice and, if desired, the sweetener. Blend on high until the mixture is smooth and uniform, about 30-60 seconds. The color should be vibrant and the texture liquid but consistent.
Prepare your ice cube trays or popsicle molds by securing the sticks or covers if necessary. Pour the blended watermelon mixture evenly into each cavity, leaving a small gap at the top for expansion.
Place the filled molds into the freezer. Allow them to freeze for at least 4 hours, or until they are completely solid and firm to the touch. You may see a slight frosty coating around the edges once frozen.
To serve, run warm water briefly over the outside of the molds to loosen the pops. Gently pull out the watermelon pops and place on a plate or serve directly. Enjoy immediately for the best icy, refreshing texture.
