Peel, core, and slice the apples.
Stack the apples in a large slow cooker (at least 6 quarts!). Shove cinnamon sticks throughout the apples, then spread brown sugar, lemon zest, and lemon juice on top.Cover and cook on high for 4-5 hours or on low for 7-8 hours. The apples should be cooked down and breaking apart. It helps if you can stir it once or twice, but you don't have to.
Use a potato smasher to mash the apples for a chunky consistency or an immersion blender to puree apples to a smooth consistency. If the apples don't easily mash or blend, they need to be cooked longer.
Taste the apples. Depending on how sweet the apples are and your own tastes, you may want to stir in additional sugar.
Turn off the crock pot, allow to cool to warm or room temperature, then store applesauce in sealed containers in the fridge for 7-10 days.