Preheat your oven to 350°F (175°C). Grease an 8x8-inch baking dish or line it with parchment paper.

In a large mixing bowl, combine the rolled oats, protein powder, baking powder, baking soda, salt, and cinnamon. Stir well.

In a separate bowl, whisk together the eggs, almond milk, honey, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and mix gently until just combined.

In a small bowl, combine the brown sugar and cinnamon for the swirl.

Pour half of the batter into the prepared baking dish, spreading it evenly.

Sprinkle half of the cinnamon swirl mixture over the first layer of batter.

Pour the remaining batter over the cinnamon swirl layer, spreading it evenly.

Sprinkle the remaining cinnamon swirl mixture on top of the last layer of batter.

Bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cake to cool in the baking dish for about 10 minutes before slicing.

Cut the cake into squares and enjoy warm or at room temperature.