I know that the list says chili powder, but that is because the site does not have an entry for Adobo. Use adobo. it's smoky and spicy and really makes the drink. It is the sauce that Chipotle peppers come packed in when canned. Check the latin foods section of your megamart.

Fill the blender about half with Ice, the rest of the way with large watermellon chunks. How much booze you add is your call, but I'd say about half a cup. Adobo amount is also a bit of personal preference, but I'd start slow; it's spicy. Say 1/2 to 1 teaspoon.

Put the Ice, watermelon chunks, light rum, adobo and orange liqueur into a blender and blend until a frozen slush. Use the ice to salt the rim, or just to balance out the sweetness of the watermelon as required.