Slice the watermelon in half horizontally.

Carefully scoop out the watermelon flesh from each half, leaving about a 1/2-inch rind to create a bowl. You can reserve the scooped-out watermelon for another use.

Use paper towels to thoroughly dry the inside of each watermelon half. This helps the jello set properly.

In a large bowl, prepare the Jello mix according to the package directions using 4 cups of boiling water and 4 cups of cold water.

Carefully pour the prepared Jello mixture into the hollowed-out watermelon halves.

Place the jello-filled watermelon halves on a baking sheet or in a shallow dish (to catch any potential spills) and refrigerate.

Chill for at least 6 hours, or until the jello is completely firm.

Once firm, slice the watermelon into wedges. For best results, make sure the slices are thick enough so the jello stands up well.