Preheat oven to 350 degrees F. Line 8x8" square baking pan with parchment paper or foil. If using foil, spray it with cooking spray.
In medium bowl, combine flour, cocoa powder, and salt. Set aside.
In large mixing bowl, beat together butter, sugar, and vanilla until creamy.
Add the eggs one at a time.
Stir dry ingredients into batter.
Pour batter into prepared pan and spread evenly.
Sprinkle with chocolate chips. Bake in preheated oven for 22-25 minutes.
When brownie layer is done baking, combine peanut butter and oil in a microwave safe bowl or measuring cup and microwave on high for 20 seconds to soften.
Pour this warm mixture over hot brownie.
Sprinkle the peanut butter covered brownies with marshmallows.
Return to oven to bake for 3 more minutes, or until the marshmallows puff.
Sprinkle puffed marshmallows with toasted pecans.