Preheat oven to 350°F. Grease a 12 cup muffin pan with cooking spray of choice. Set aside.
Place all of the muffin ingredients, except for the pecans, in the order listed, in a high powered blender. If you do not have a high powered blender you can use oat flour instead of rolled oats and mix the ingredients together with a hand mixer. Blend for 60 seconds or until a smooth batter forms. Stir in the pecans or walnuts.
Fill the muffin cups 3/4ths full with the batter, dividing it evenly amongst the cups. In a small bowl combine all the streusel ingredients. Sprinkle over top of each batter filled muffin cup.
Place the pan inside the preheated oven and bake for 16 minutes or until a toothpick is inserted and comes out clean. Let cool for 5 minutes before running a butterknife along the sides of the muffin cups, carefully remove each muffin and serve warm.
Notes
Recipe Notes:The streusel topping is completely optional, it elevates the recipe, but they're great without it too!