Brown the butter in a saucepan over medium heat until nutty and amber, 5 to 7 minutes. Cool 10 minutes.
Whisk the warm brown butter with brown sugar and granulated sugar until glossy.
Stir in pumpkin puree and vanilla until smooth.
In a bowl, whisk flour, oats, baking soda, baking powder, salt, cinnamon, and pumpkin pie spice.
Add dry ingredients to the pumpkin mixture and mix just until no dry spots remain.
Fold in chocolate chips and pecans, if using. Chill the dough for 30 minutes.
Heat oven to 350°F. Line two baking sheets with parchment paper.
Scoop 2-tablespoon mounds of dough, spacing about 2 inches apart. Gently flatten the tops.
Bake 12 to 14 minutes, until edges are set and centers look just done.
Cool on the sheet for 5 minutes, then transfer to a rack to finish cooling.