Cut the watermelon in half, then use a spoon to scoop all the vibrant pink flesh into a large bowl. Do your best to remove any visible seeds as you go. Break the bigger pieces into smaller chunks.
Transfer those watermelon chunks into your blender or food processor. Blend it up until it's completely smooth and liquidy.
In a separate bowl, pour in your tequila, fresh lime juice, simple syrup, chili powder, and sea salt. Give it a good whisk or stir to make sure everything is combined.
Pour the smooth watermelon puree into the bowl with the tequila mixture. Stir it gently but thoroughly until it's all one beautiful, consistent pink.
Carefully pour this delicious mixture into your popsicle molds. Don't fill them all the way to the absolute top; leave a little bit of space for expansion as they freeze.
Insert your popsicle sticks into the molds. If your molds have lids with stick slots, pop those on. If not, you can cover the top with foil and poke the sticks through the foil to help them stay straight.
Place the filled molds into the freezer. Let them freeze for at least 6 hours, or ideally until they are completely solid. Overnight is usually best.
When ready to enjoy, run the outside of the popsicle mold under warm water for just a few seconds. This helps loosen the edges.
Gently pull the popsicle from the mold.