Combine the granola (break up any large clumps), peanut butter, syrup, and cinnamon, and any of the optional ingredients in a large bowl and work together using clean hands.
Rinse of your hands and form the mixture into packed 1-inch balls with slightly damp hands. If things get sticky, rinse and dampen your hands as needed.
Arrange on a wax paper or parchment-lined plate and refrigerate for 30 minutes or more to allow them to firm up. Or, if you can’t wait, pop into the freezer for 10 to 15 minutes.
Keep any unused portion in the fridge, in a covered container.