Preheat and prep. Heat your oven to 350°F (175°C).
Line a 12-cup muffin pan with paper liners or lightly grease with oil spray.
Mix the dry ingredients. In a large bowl, whisk flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice until evenly combined. This helps avoid clumps and overmixing later.
Whisk the wet ingredients. In a separate bowl, whisk pumpkin puree, maple syrup, brown sugar, Greek yogurt, eggs, vanilla, and oil until smooth and glossy.
Combine gently. Pour the wet mixture into the dry ingredients. Stir with a spatula just until you no longer see dry streaks.
A few small lumps are fine.
Fold in the chocolate chips. Add mini chocolate chips (and nuts, if using). Fold gently to distribute without overworking the batter.
Portion the batter. Divide evenly among the 12 muffin cups, filling each about 3/4 full. For a bakery-style dome, you can fill a bit higher.
Bake. Place the pan on the center rack and bake for 18–22 minutes.
The muffins are done when a toothpick comes out mostly clean with a few moist crumbs.
Cool. Let muffins cool in the pan for 5 minutes, then transfer to a wire rack. Cooling helps set the crumb and keeps them from getting soggy.
Optional finishing touch. While warm, sprinkle a few extra chocolate chips on top for a pretty finish that lightly melts into the surface.