Preheat oven to 350 degrees F. Spray a 9x13- inch baking dish with nonstick cooking spray; set aside.
In a large bowl or stand mixer, cream together butter substitute, yogurt and Truvia. Mix in egg and vanilla.
Add flour, protein powder, baking powder and salt and mix until combined then spread evenly in prepared pan. Bake for 22 minutes, then remove from oven and let cool.
Combine all frosting ingredients and mix until smooth, then spread on top of cooled bars. Place in the refrigerator to set then cut into bars.