Preheat oven to 375. Line muffin tin with liners or spray with oil.
In small bowl, mix flaxseed with 3 tbsp warm water. Set aside for 5 mins to form a flax egg.
While the flax egg is forming, mash a ripe banana with a fork until there aren't any lumps.
Combine mashed banana, peanut butter, almond milk and vanilla extract and mix until well combined. Add in flax egg.
Add rolled oats & almond flour to banana mixture and stir. If you're using add-ins, now would be the time to mix them in.
Pour mixture into muffin tins to make 9 muffins. Bake for 12-15 minutes until toothpick comes out clean.
Cool in muffin tin for 10 minutes then transfer to wire rack to cool completely.
Once they are cooled, enjoy!
Store in fridge for up to a week.