In a small saucepan (or microwave safe bowl) mix peanut butter, honey, water, vanilla, and cinnamon. Heat over low (or for 30 seconds in the microwave) until the honey melts and the mixture can be stirred smooth.
In a medium bowl, mix oats, wheat bran, and ground flax. Pour peanut butter mixture over the oat mixture and mix with a spatula until everything is evenly coated and moist.
Take a rounded tablespoon full of the mixture and shape it into a ball using your hands. Continue until all the mixture has been used.
Store the granola bites in an air-tight container in the refrigerator for up to a week.