Preheat oven to 350°F (175°C). Line a baking sheet with parchment.

Whisk oats, flour, cocoa, baking soda, salt, and cayenne in a bowl.

Beat butter and brown sugar until creamy; add egg and vanilla and mix.

Stir dry ingredients into wet until combined, then fold in chocolate chips.

Scoop tablespoon-sized balls onto sheet, flatten slightly, and bake 9–11 minutes.

Cool 5 minutes on the sheet, then transfer to a rack.