1Heat oven to 350º. Press dry crust from lemon bar mix in bottom of square pan (8x8x2 or 9x9x2 inches). Bake 10 minutes.
2Add enough water to lemon juice to equal 1/2 cup. Place filling from lemon bar mix and protein powder in large bowl. Stir in egg product and lemon juice mixture with wire whisk until smooth. Pour filling over hot crust.
3Bake 25 to 30 minutes or until top just begins to brown and center is set. Cool completely, about 2 hours. Sprinkle with powdered sugar. For bars, cut into 4 rows by 4 rows.