Prep the pan: Heat oven to 350°F (175°C). Line a 12-cup muffin tin with liners or grease well.
Blend the oats: Add 2 cups rolled oats to a blender or food processor. Pulse until they become a fine oat flour.
Mix the wet ingredients: In a large bowl, whisk 1 cup pumpkin puree, 2 large eggs, 1/3–1/2 cup maple syrup (to taste), 1/3 cup almond milk, and 1 teaspoon vanilla until smooth.
Add dry ingredients: Stir in the oat flour, 1 teaspoon baking powder, 1/2 teaspoon baking soda, 1 1/2 teaspoons pumpkin pie spice, and 1/4 teaspoon salt.
Mix just until combined.
Fold in extras: If using, gently fold in 1/2 cup dark chocolate chips or 1/2 cup chopped nuts.
Fill the cups: Divide the batter evenly among the 12 wells. The batter will be thick; that’s okay.
Bake: Bake 16–20 minutes, until the tops spring back and a toothpick comes out clean or with a few moist crumbs.
Cool: Let muffins cool in the pan for 5 minutes, then transfer to a rack to finish cooling. This helps them set and stay tender.