Prepare waffle mix according to package directions. Bake in a lightly greased waffle iron according to manufacturer's instructions. Let waffles cool. (You can do this step a day in advance! Just store waffles in an airtight container or Ziploc bag.)
Preheat oven to 350*F and lightly grease a 9x13 inch pan with cooking spray.
Whisk together milk, eggs, vanilla, and cinnamon.
Arrange a layer of waffles in the bottom of the pan. Break waffles into halves or fourths and overlap if you need to.
Pour half of milk/egg mixture over waffles. Top with another layer of waffles and remaining milk mixture.
Cover and refrigerator for at least 2 hours, or overnight.
Bake for 30-35 minutes or until lightly golden brown on top.