In a medium mixing bowl, add Quest Protein Powder®, almond milk, egg whites, eggs, cocoa powder, sweetener, almond flour, oat flour, baking powder, and salt. Whisk until smooth.
Line the bottom of two 9-by-13-inch cake pans with parchment paper.
Lightly coat parchment paper with cooking spray.
Evenly distribute batter between two cake pans.
Bake for 16 to 18 minutes.
Remove and cool for 20 minutes.
Filling
Break Quest Bars® into small pieces and place in a medium microwave-safe bowl.
Add almond milk, sweetener, and salt. Microwave for 1 minute.
Stir together, and let cool for 5 minutes.
Stir in Quest Protein Powder® until thick, and set aside.
Icing
In a microwave-safe bowl, add sweetener and almond milk, and microwave for 30 seconds.
Add mixture to a food processor with Quest Protein Powder®, sour cream, cream cheese, and vanilla extract, and process until smooth.
Transfer mixture into a medium mixing bowl.
Add food coloring (if using), and stir to combine.