Step 1: Preheat the Oven

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

Step 2: Prepare the Cake Batter

1. In a large mixing bowl, combine the rolled oats, protein powder, baking powder, baking soda, salt, and cinnamon. Stir to combine.
2. In a separate bowl, whisk together the eggs, almond milk, honey, and vanilla extract until smooth.
3. Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.

Step 3: Prepare the Cinnamon Swirl

1. In a small bowl, combine the brown sugar and cinnamon. Set aside.

Step 4: Assemble the Cake

1. Pour half of the batter into the prepared baking dish and spread it evenly.
2. Sprinkle half of the cinnamon swirl mixture over the batter.
3. Pour the remaining batter over the cinnamon swirl layer and spread it evenly.
4. Sprinkle the remaining cinnamon swirl mixture on top.

Step 5: Bake the Cake

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

Step 6: Cool and Serve

1. Allow the cake to cool in the baking dish for about 10 minutes before slicing.
2. Cut into squares and enjoy warm or at room temperature. It can be served plain or with a drizzle of yogurt or additional honey.