Preheat the oven to 375 degrees F. Coat a medium baking dish with cooking spray. Spread pumpkin chunks in a single layer and roast for 30-40 minutes (depending on the size of the chunks), or until the pumpkin is fork-tender and the top has caramelized a bit. Place the chunks in a food processor and pulse until smooth. If the puree is watery, drain it in a cheesecloth-lined colander. It should make about 1 cup of pumpkin puree. Set aside. (You can use 8 oz. pre-made canned pumpkin puree instead).
Preheat the oven to 350 degrees F. Line two muffin pans with 14 paper liners. Set aside.
To make the streusel topping, add the flour, oats, sugar and cinnamon in a medium bowl and mix until combined. Rub in the butter with your fingers until the mixture is crumbly. Stir in the maple syrup. Set aside.
Put the oats in a food processor and process until the oats look like flour. Place oat flour, whole wheat flour, all-purpose flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg and cloves in a large bowl and whisk together. Set aside.
In a separate bowl, combine sugar and eggs, and beat until well blended. Add oil, buttermilk, vanilla and maple syrup to mixture and whisk to combine. Add pumpkin puree and whisk to combine. Pour the wet ingredients into the dry ingredients and stir, using a wooden spoon or rubber spatula, until just combined, being careful not to over-mix. Gently stir in the chopped cranberries.
Fill muffin cups about 3/4 of the way full. Sprinkle each muffin with oat streusel topping. Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Let cool in pan for 10 minutes before removing to a wire rack to cool completely. Enjoy!