Preheat your oven to 350° Fahrenheit (176° Celsius). Line two baking sheets with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, ground ginger, allspice, cloves, nutmeg, and salt. Set aside.
In another bowl, whisk together the melted butter and brown sugar until well combined. Then whisk in the egg and vanilla extract until smooth.
Sift the dry ingredients into the wet mixture. Stir gently until just combined. Fold in the oats and chopped pecans.
Cover the dough with plastic wrap and chill in the refrigerator for about 15 minutes.
Scoop portions of dough onto prepared cookie sheets, leaving enough space between each ball.
Bake for about 12–15 minutes until golden on the bottom but slightly under-baked in the center. Let cool on wire racks.