Preheat the Oven: Preheat your oven to 350°F (175°C) and line a muffin tin with muffin liners or spray with non-stick spray.
Mix Dry Ingredients for Muffins: In a large mixing bowl, combine the flour, vanilla protein powder, baking powder, pumpkin pie spice, and salt. Whisk until well blended.
Combine Wet Ingredients for Muffins: In a separate bowl, whisk together the pumpkin puree, Greek yogurt, milk, honey or maple syrup, and eggs until smooth.
Combine Muffin Mixtures: Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix.
Prepare the Crumble Topping: In a small bowl, combine rolled oats, almond flour, brown sugar, cinnamon, and melted coconut oil. Mix until crumbly.
Fill Muffin Tin: Divide the muffin batter evenly among the muffin cups, filling each about 2/3 full. Sprinkle the crumble topping generously over each muffin.
Bake: Bake for 18-20 minutes or until a toothpick inserted in the center comes out clean.
Cool and Enjoy: Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.