There are several things you can try, do you have a hand mixer? or a table top? or just a whip? All are fine it's just a matter of ease.Try this:
Put all the ingredients together
except the eggs.
Add a bit more water or milk or a combo of the two until it comes to a "pancake" type consistency. This is gonna vary, you'll have to play with it.
In a seperate bowl whip the egg whites to soft peaks (video how-to attached)
Fold (not stir) in the eggs to the other ingredients (video how-to attached)
This is a little more time consuming/work, say 5 extra minutes, but it should be worth it. They might rise a little so only fill your cups/pan 3/4 of the way. I have never made protien bars, cakes but as a general rule this should work. This is the same way meringue, mousse, souffle get their "airyness". Give it a try and let me know how it goes.
Eggs beat to peaks by machine:
How To Beat Egg Whites - YouTube
Eggs beat to peaks by hand:
How To Whip Egg Whites - YouTube
Folding egg whites into something:
如何拌勻蛋白霜 How To Fold-in Egg Whites - YouTube