Preheat the oven to 180°C (356°F).
In a bowl, mix protein powder, cocoa powder, baking powder, and salt.
In another bowl, whisk together eggs, unsweetened milk, stevia, and vanilla extract.
Combine the dry ingredients with the wet ingredients and mix until well combined.
Add coconut oil to complete the batter.
Pour the batter into a loaf pan and smooth the top.
Bake in the oven for 18–20 minutes.
Let it cool, then cut into desired sizes.