Poke holes in the sweet potato with a fork or skewer and microwave until soft, about 15 minutes. Let cool completely in the fridge. Scoop 1 cup of the sweet potato flesh into a large bowl and whip with a fork until evenly mashed. Reserve any extra sweet potato for another use.
Preheat the oven to 375 degrees F. Line a muffin tin with 12 liners and spray with nonstick cooking spray.
Whisk together the pastry flour, whole-wheat flour, baking powder, allspice, salt, baking soda and cinnamon in a large bowl.
Add the eggs to the sweet potato and whisk to combine. Whisk in the melted butter, milk, oil and yogurt.
Pour the wet mixture into the dry ingredients and gently fold together until just mixed. Fold in the chocolate chips.
Evenly divide the batter between the prepared muffin cups and sprinkle the tops with the oats. Bake until golden and a toothpick inserted into the center of each muffin comes out clean, about 35 minutes. Allow to cool slightly on a rack.