https://thepioneerwoman.com/cooking/my-moms-muffins/
We've liked this recipe a lot recently. I leave out the nuts and raisins for our personal tastes. It makes a lot of batter too - when I double it I end up with 24 muffins plus a couple of mini loaves.
I have not tried adding protein powder to baking recipes. I have made a few recipes that use Greek yogurt. The recipe I posted could probably do well with Greek yogurt in place of some of the applesauce.