Lightly grease an 8x8-inch pan or silicone mold with light oil or cooking spray, wiping away excess with a paper towel.
Pour ½ cup cold grapefruit juice into a small bowl. Sprinkle the gelatin evenly over the top. Let it sit for 5 minutes until completely thickened and spongy.
Add the remaining 1½ cups grapefruit juice and optional lemon juice to a heavy bottom sauce pan. Warm over low heat until steaming, but absolutely do not boil.
Remove saucepan from heat. Stir the honey into the warm juice, then add the bloomed gelatin chunk and whisk gently until fully dissolved and smooth.
Pour into the prepared pan. Refrigerate for 4 to 6 hours, or until very firm and completely set into a soft gel.
Run a knife around the edges to loosen, then cut into small cubes to serve as a pre-meal volume filler.
