Cut the watermelon plank into quarters. Using a paring knife, cut a slit in the bottom of the rind of each quarter and insert a popsicle stick into the watermelon slice.
Lay the watermelon slices on a rimmed sheet tray. Pour tequila, orange liqueur and lime juice into the tray and shake it around to “mix” the liquids. Freeze for 4 hours or overnight.