Add the fresh watermelon to a blender and process until smooth.

Pour the blended watermelon through a fine mesh strainer into a Pyrex measuring cup or similar. You should have about 2 cups / 480 milliliters of juice. Skim any white foam from the top of the juice and discard.

Pour half of the watermelon juice into a saucepan, leaving the other half behind in the measuring cup. Sprinkle the unflavored gelatin powder over the reserved juice. Let it sit for a few minutes until it is absorbed by the liquid.

While the gelatin is blooming, warm the watermelon juice in the saucepan over a low medium heat. You do not want or need to bring it to a boil. Add the bloomed gelatin to the warm watermelon juice, whisking until it melts and combines into a smooth liquid. Stir in the lemon juice and, if using, the honey, to taste.

Pour the gelatin mixture into molds or a refrigerator & knife friendly baking dish. Let chill for at least 2 hours before removing from the molds or slicing into pieces.