Preheat the oven to 350 degrees Fahrenheit and line a muffin tin with 11 paper liners.

Transfer the oats, pumpkin pie spice, baking powder, and sea salt to a high-speed blender or a food processor and blend until a flour forms, about 60-90 seconds.

Transfer the remaining ingredients to the food processor and blend until a smooth muffin batter forms. Note: if you're using flour instead of oats, mix the dry ingredients and the wet ingredients in two separate bowls before combining them into one large bowl.

Pour the pumpkin batter into the prepared muffin pan, filling the muffin cups most of the way up.

In a small bowl, stir together the streusel topping ingredients. This mixture should be thick. That is normal.

Sprinkle the streusel topping mixture on top of the muffin batter. Bake on the center rack of the preheated oven for 25 minutes, or until the muffins are fully cooked. Insert a digital thermometer into the center of one of the muffins. If it reads 190 degrees F or higher, the muffins are ready!

Allow the pumpkin streusel muffins to cool to room temperature before peeling off a muffin paper to enjoy one. If you try peeling the muffin liners off when the muffins are still warm, you will lose some muffin to the paper. Enjoy one with a cup of coffee or tea for a lovely afternoon snack! Or, pair one with a protein source for breakfast.