Mix flax egg, set aside. Combine dates and 1/2 cup water, let soak.
In food processor fitted with an S-blade, process rolled oats into coarse flour. Transfers to mixing bowl, add baking powder and matcha powder.
Cut hard ends off of lemon, slice in half and remove seeds (do not peel). Add to food processor along with dates (including soaking water) and vanilla extract. Process until smooth, stopping to scrape down sides as needed.
Add lemon mixture, flax egg and goji berries to dry ingredients, mix until combined.
Pour dough into 6 non-stick muffin tins. Bake for 25 minutes or until golden.