Heat oven to 350°F. Line two 8 or 9-inch round cake pans with aluminum foil, allowing foil to extend over sides of pans. Spray with cooking spray. For topping, combine oats, flour and brown sugar in large bowl. Cut in peanut butter and margarine with two knives until mixture is crumbly; set aside. For brownies, melt chocolate chips and margarine in medium saucepan over low heat, stirring frequently. Remove from heat; cool slightly. Stir in sugar and vanilla. Add eggs; mix well. Add combined flour, oats, baking powder and salt; mix well. Divide batter evenly between pans. Sprinkle with reserved topping, patting gently. Bake 22 to 24 minutes for 8-inch pan (20 to 22 minutes for 9-inch pan) or just until center of brownie is set. (Do not overbake.) Cool completely in pans on wire rack. To assemble, spread softened ice cream evenly over one brownie while still in pan. Lift second brownie out of pan; remove foil. With topping side up, place brownie on top of ice cream, pressing gently. Cover and freeze several hours or overnight. Remove from freezer 10 to 15 minutes before cutting. Lift from pan using foil edges. Remove foil; cut into wedges. Individually wrap wedges and store in freezer.