Prepare a small canning pot and two half pint jars.
Combine mashed blueberries, sugar and sliced ginger in a bowl or measuring cup. Let sit for at least an hour and up to 24 hours to give the ginger time to infuse its flavor into the fruit. If you’re going for a longer maceration time, pop the fruit into the fridge.
When you’re ready to make the jam, pour the fruit into a medium pot. Bring to a boil and add the lemon zest and juice. Cook for 10-20 minutes (time depends on moisture level in fruit, humidity, power of stove, etc.) until jam approaches 220 degrees and appears to pass the plate test.
When jam is finished cooking, remove pot from heat and stir in the candied ginger. Pour into prepared jars. Wipe rims, apply lids and rings and process in a boiling water canner for 10 minutes.
Check seals when cool and store unopened jars in a cool, dark place.