Prep the oven and pan. Heat oven to 375°F (190°C). Line a 12-cup muffin tin with liners or grease well.
Mix wet ingredients. In a large bowl, whisk pumpkin, eggs, oil, brown sugar, maple syrup, vanilla, and milk until smooth.
Add dry ingredients. Sprinkle oats, flour, baking powder, baking soda, cinnamon, nutmeg, and salt over the wet mixture.
Stir gently until just combined. Do not overmix.
Fold in extras. If using chocolate chips, nuts, or raisins, fold them in now.
Fill the cups. Divide batter evenly among 12 muffin cups. The cups will be fairly full. Sprinkle tops with a few oats or coarse sugar if you like.
Bake. Bake 16–20 minutes, until the tops spring back and a toothpick comes out with a few moist crumbs.
Cool. Let muffins rest in the pan for 5 minutes, then transfer to a wire rack to finish cooling.