Preheat your oven to 350°F and line three slots of a muffin tin with parchment liners.
In a medium bowl, whisk together the egg, 0.25 cup of the Greek yogurt, vanilla extract, and 0.5 tablespoon of the maple syrup until smooth.
Stir in the vanilla protein powder, 0.125 cup of the oat flour, baking powder, sea salt, and lemon zest until a thick batter forms.
Gently fold the fresh blueberries into the batter using a spatula to avoid crushing them.
In a small separate bowl, combine the remaining 0.125 cup of oat flour, coconut oil, cinnamon, and 0.25 tablespoon of the maple syrup to create a crumbly texture.
Distribute the muffin batter evenly among the three lined tins and sprinkle the oat crumble over the top of each muffin.
Bake for 18 to 22 minutes or until the tops are golden and a toothpick inserted into the center comes out clean.
Whisk together the remaining 0.25 cup of Greek yogurt, lemon juice, and the remaining 0.25 tablespoon of maple syrup to create a smooth glaze.
Allow the muffins to cool slightly on a wire rack before drizzling the zesty lemon glaze over the tops.