Stir the zucchini and sugar together in a large pot over medium heat until the sugar has dissolved and the mixture begins to boil, about 10 minutes. Stir in the lemon juice and gelatin, and continue simmering 5 minutes more, stirring constantly.
Ladle the hot jam into 6 hot, sterilized half-pint canning jars leaving 1/4 inch headspace. Wipe the rim and jar threads with a clean, damp cloth. Center lid on jar and screw the ring down firmly. Place into a boiling water canner covered by 2 inches of boiling water. Process for 10 minutes. Remove from the canner, and allow to cool to room temperature, and refrigerate any jars that do not seal.