Preheat oven to 350 degrees. Line 2 baking pans with parchment paper.
Combine the flour, baking powder and baking soda in a large bowl. In a separate bowl beat the butter and both sugars with a mixer on medium high speed until fluffy. Beat in the eggs one at a time on medium speed, then beat in the vanilla. Add the flour mixture and beat on low until combined.
Stir in the oats, 1 cup each of chocolate chips, pecans and marshmallows into the dough with a wooden spoon. Drop heaping tablespoonfuls of the dough onto the prepared baking sheets about 3 apart. Bake the cookies in batches until golden, 10-12 minutes. Transfer to racks to cool.
To make topping - Combine the remaining chocolate chips and marshallows, half and half and cayenne pepper in a saucepan over medium heat; cook, stirring until the mixture is smooth, about 5 minutes. Remove from heat. Stir in the remaining pecans. Drizzle mixture over the cookies and let set, about 4 hours.