Preheat the oven to 350 degrees Fahrenheit. Line a 12-tin muffin tray with paper liners. Prepare your flax eggs by combining ground flaxseeds and 6 tablespoons water in a small bowl. Stir and set aside for 5 minutes.
In a large bowl, combine almond flour, arrowroot, baking soda, baking powder, cinnamon, and salt. Whisk to combine.
Add lemon juice, mashed banana, melted coconut oil, vanilla extract, maple syrup and flax eggs. Stir until all ingredients are completely incorporated.
Fold in 1/2 cup of the walnuts. Divide muffin batter evenly amongst muffin cups, between about 1/2 to 3/4 of the way full. Sprinkle remaining chopped walnuts on top. Bake for 25-30 minutes. Muffins should be a golden brown and a toothpick comes out mostly clean.
Remove from oven and place muffin tin on a wire rack to cool. Allow muffins to cool completely (especially before removing from liner).Store muffins in an airtight container for 2-3 days.