HEAT oven to 350°F. Coat 12-inch pizza pan with no-stick cooking spray.
BEAT peanut butter and shortening in large bowl with electric mixer until blended. Add brown sugar, egg, water and vanilla. Mix on medium speed until combined. Beat in pancake mix on low speed until evenly moistened. Spread evenly on bottom of prepared pan.
BAKE 10 to 12 minutes or until edges are light brown. Cool completely.
STIR 1 cup frosting, red color and yellow color in small bowl to make orange color. Spread over entire top of cookie. Place 1/4 cup plain vanilla frosting in resealable plastic bag. Microwave on HIGH 10 seconds or until soft. Cut small corner off bag. Draw outside lines and inside lines for a spider web on top of frosting. Cut through with toothpick or knife to make design. Make spiders on web using black gel or place candy or plastic spider on top. Cut into wedges to serve.