Preheat your oven to 350°F (175°C). Grease a muffin tin or line with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In another bowl, mix the mashed sweet potatoes, brown sugar, vegetable oil, eggs, and vanilla extract until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in the chopped pecans.
Spoon the batter into the prepared muffin tin, filling each cup about ⅔ full.
Bake for 20-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.