Start by making the flax egg: in a small bowl combine flaxseed and water and allow to sit for a few minutes, until thickened and a gel like texture.
Preheat oven to 375 and spray a muffin tin with cooking spray or line with muffin liners and set aside.
In a bowl combine the flour, brown sugar, baking powder, baking soda, cinnamon, and salt.
In another bowl combine vanilla extract, applesauce, vegetable and flax egg.
Add the dry ingredients into the applesauce mixture. Stir to combine gently.
Divide batter between muffin cups (they'll be 3/4 full)
Make streusel topping by melting butter in a microwave safe bowl, then add in the flour, brown sugar and cinnamon. Top each muffin with a little streusel.
Bake for 16-20 minutes, or until slightly starting to brown around edges or a toothpick comes out clean when poked into the center of a muffin.
Remove from oven and allow to cool a little.
Enjoy, or allow to cool completely before putting in a freezer bag or container and freezing. These are good in the freezer for up to 3 months.