Preheat your oven to 350° Fahrenheit. Line a muffin tin with 12 muffin liners.
Combine the melted coconut oil, brown sugar, pureed pumpkin, and eggs in a medium sized bowl. Mix until fully combined and smooth.
Add the cinnamon and baking powder to the batter and mix well.
Add the oat flour, rolled oats, and chopped walnuts to the batter. It will be really thick.
Stir in the almond milk and stir the batter until it is fully combined. Set aside.
In a separate bowl combine all of the ingredients for the crumble. Mix until it is crumbly and has a consistent texture.
Scoop the muffin batter into the prepared muffin tins and sprinkle with the crumble topping.
Bake for 20-25 minutes or a toothpick inserted into the center of the muffins comes out mostly clean with only a few crumbs.
Enjoy! The muffins will keep in an airtight container at room temperature for 2-3 days or in the freezer for up to 2 months.