Heat oven to 350 degrees F. Lightly grease a 9×13-inch pan and set aside.
In large bowl combine all oatmeal layer ingredients except egg and vanilla. Mix until crumbly. Reserve 3/4 cup loose crumbs for topping. Add egg and vanilla to remaining crumbs and mix well.
Pat mixture to bottom of prepared pan. If dough is sticky, dust hand with flour before patting into pan or cover hand with a small plastic bag.
To prepare fudge layer, heat butter, sugar, and chocolate chips in medium saucepan over low heat, stirring constantly, just until butter and chocolate are melted.
Remove from heat and beat in eggs and vanilla until well combined. Stir in flour and walnuts and mix well. Spread mixture over peanut butter layer, and top with reserved crumbs.
Bake 20 to 25 minutes or until lightly browned. Cool and cut into bars before serving.