Preheat the oven to 350°F. Line a loaf pan with parchment paper and set aside.
In a large bowl, mix together the flour, baking powder, baking soda, cinnamon, stevia and brown sugar until combined.
In a medium bowl, beat the eggs. Mix in the protein shake and oil until smooth.
Slowly mix in wet ingredients into the dry ingredients until just combined. Do not overmix.
In a small bowl, mix together the crumb topping ingredients. Set aside for now.
Pour the batter into the prepared loaf pan and bake in the preheated oven for 20 minutes. Top with the crumb topping. Return to the oven for an additional 25-35 minutes, or until a toothpick inserted near the centre comes out clean.
Allow to cool in the pan for around 15 minutes before transferring to a wire rack to cool completely.