Preheat oven to 350 degrees. Prep muffins tins with spray.

In a medium mixing bowl stir together the mashed banana, avocado oil, vinegar and milk. Add the Cassava flour, baking powder, baking soda, and cinnamon. Slowly stir with large spoon or whisk. Fold in the collagen if using. 

Spoon the batter into the prepared muffin tins. About 2-3 tablespoons for each muffin. Top with frozen blueberries. 

Bake for 12-15 minutes or until golden brown on the edges.