Preheat the oven to 350℉ and line an 8x8-inch baking dish with parchment paper. Set aside.
Prepare the streusel topping. Add the rolled oats, flour, protein powder, brown sugar, butter, and almond extract to a mixing bowl. Use a fork and cut the ingredients together until a crumbly texture forms. This may take a few minutes. Set aside for later.
Next, add the flour, baking powder, and salt into a bowl and toss together. Set aside.
In a separate bowl, mix the wet ingredients, including brown sugar.
Slowly add the dry ingredients to the wet and mix until combined. Fold in the frozen raspberries.
Transfer the batter to the lined baking dish and top with the streusel topping. Bake the cake for 20 minutes, cover it with a tin foil tent, and bake for another 20 minutes. Remove the cake from the oven if a toothpick inserted into the middle comes out clean.
Let the cake cool for 10 minutes, then remove it from the baking dish and serve.