Preheat the oven to 325F. Fill a regular muffin pan with parchment liners. Set aside.In a medium mixing bowl, combine the almond meal, oat flour, baking powder, baking soda, cardamom, and psyllium.In a separate medium mixing bowl, combine the chia egg, coconut milk, lemon juice, maple syrup, vanilla extract, olive oil, and lemon zest. (Tip: if your coconut milk is separated into water and fat, combine all liquid ingredients in this recipe together in a blender -- or use a hand blender, fully submerged in the liquid ingredients).Add the liquid mixture to the dry mixture, combining gently until the mix is fully saturated and even.Add the frozen blueberries and stir to incorporate.Fill each of the muffin liners 3/4 full with batter. For the streusel: In a small bowl, mix together the oats, coconut sugar, walnuts, salt, and olive oil.Sprinkle the streusel over top of each muffin.Bake for 20-25 minutes, rotating once half way through. The muffins are done when the streusel is golden and a knife inserted in the center comes out clean.Let cool to room temperature, at least 20 minutes.Unwrap and enjoy!