Preheat oven to 400F/ 200C and line a 12-cup muffin tin with paper liners or spray well with non-stick spray.
Add all the streusel ingredients to a medium-sized bowl and combine with a fork or your fingers until crumbly. Set in the refrigerator.
Begin by making the flax egg. Combine 1 tbsp ground flax seeds with 3 tbsps of water in a small bowl and set aside for 5 minutes until thickened.
In a large bowl, add the flour, oats, baking powder, baking soda, salt, cinnamon, ginger, and nutmeg and stir to combine. Set aside.
In a medium bowl, add the oil, applesauce and maple syrup and stir to combine. Then whisk in the eggs and vanilla, followed by the yogurt. Whisk until smooth. Set aside.
Add the grated and chopped apples to the dry ingredients and stir to combine.
Make a well in the center of the dry ingredients and add the wet ingredients plus the flax egg. Fold the wet ingredients into the dry until just combined.
Fill each muffin cup about 3/4 full, then spinkle the streusel topping evenly on the muffins.
Bake for 10 minutes then turn the heat down to 350F/177C and continue to bake about 10 minutes longer until the muffins spring back to the touch or a toothpick inserted into the center comes out clean.
Let cool in the muffin pan on a wire rack then enjoy!
*Muffins will keep in an airtight container at room temperature for 2 days or up to a week in the refrigerator. Alternately, you can freeze them in a freezer-safe container for up to 2 months and bring back to room temperature or re-heat as needed.