Prepare the ingredients. Cut the zucchini into small cubes. Grate the zest from the lemon on a fine grater. Cut the lemon into squares. Transfer the zucchini to a saucepan for cooking jam, sprinkle with sugar. Let stand for 10 minutes to release the juice.
Cook the jam. Place the pan on medium heat, bring to a boil, reduce heat, add lemon with zest, cook for 15 minutes. Turn off heat, leave for 10 hours. Place the pan back on the stove, bring to a boil over low heat, cook for 10 minutes, turn off heat. Let stand for about 6 hours.
Finish cooking. Put the pan on low heat, bring to a boil, simmer until thick for 15-20 minutes, stirring occasionally. Pour the finished jam into jars and roll up the lids.