PREHEAT oven to 350°F. Mix flour and baking soda; set aside.
BEAT margarine and sugar in large bowl with electric mixer on medium speed until light and fluffy. Add egg and vanilla; mix well. Gradually add flour mixture, beating until well blended after each addition. Stir in chocolate chips and peanuts. Spread into lightly greased 8-inch square baking pan.
BAKE 25 to 30 min. or until toothpick inserted in center comes out clean. Cool completely in pan on wire rack. Cut into 16 squares to serve.