Preheat oven to 400F. Spray muffin liners with non-stick cooking spray.
Make streusel topping first: mix oats, brown sugar and cinnamon together. Once combined, cut in butter. We use 2 butter knives and literally "cut" the butter into the mixture. When you are done your streusel should resemble small crumbles.
For the muffins, mix together dry ingredients: oats through salt.
Slowly mix in applesauce, milk, oil, vanilla and egg. Stir until well combined.
Use a large baking scoop to fill prepared muffin cups ¾ full.
Sprinkle a generous amount of streusel on the top of each muffin.
Bake at 400F for 15 to 18 minutes or until cooked through.
