Peel the bananas and slice them roughly. (I measured my bananas to be 3.5 cups after slicing.) Transfer sliced bananas to a wide shallow pot and add cinnamon sticks, sugar, and lemon juice.
Cook jam for 30 minutes on medium-low heat until bananas are soft and mushy. At this stage, you can mesh the jam with potato masher. Or remove the cinnamon stick and blend the jam with the immersion blender for a smooth jam.
When the jam is closing the setting point, jam will thicken and get glossy. Do a cold plate test by dropping a teaspoon of jam on a cold plate. Draw a line. The line shouldn't meet. The banana jam is ready.
Transfer hot jam to clean dry jars seal the lids and turn the jars upside down. This will create a vacuum seal. Let it set to room temperature for 12 hours then transfer to fridge or freezer.