Preheat the oven to 350F and grease or line a muffin tin. Add 1 tablespoon of ground flax to a small bowl with 3 tablespoons of water; set aside for 5 minutes to thicken.
Add the oat flour, cacao powder, Amazing Grass, baking soda, baking powder, and salt to a large bowl. Whisk until well incorporated.
In a separate smaller bowl, mix the applesauce, sugar, peanut butter, milk, apple cider vinegar, and thickened flax egg together. Form a well in the center of the dry ingredients, then pour in the wet ingredients. Mix until well-combined.
Divide the muffin batter evenly between the 12 muffin tins, then top with chocolate chips if desired. Bake for 22-25 minutes in the middle rack of the oven. Let the muffins sit for 5 minutes, then transfer to a cooling rack to let cool completely.
Store at room temperature in a container with a loose-fitting lid for up to 5 days, or store in the freezer for up to 2 months