This is a versatile recipe.  I’ve used diced pears instead of apples and that works well.  I’ve also made them many times without the crumb topping–that yields a muffin with less sugar and they are great without it. The crumb topping just adds an extra yumminess.  You can also use all whole wheat flour, but I prefer to have the oat flour in there to help lower the glycemic load.  I’ve even made them with all oat flour and it works if you need them to be gluten-free.  The texture isn’t as great, but they are still good. Also, I have made these with flax eggs and it does work.  I prefer the results I’ve gotten from using eggs, though.