1. Preheat oven to 425°. Line a 15- x 10-inch pan with foil; grease. Combine first 6 ingredients in a large bowl. Lightly grease hands, and press mixture into pan. Bake for 12 to 15 minutes or until golden brown. Cool completely on a wire rack.
2. Melt chocolate and shortening together in a medium saucepan or double boiler over low heat, stirring constantly until smooth. Spread mixture evenly over oat base, and sprinkle with chopped nuts. Cover loosely, and chill in pan until chocolate is firm. Lift foil and candy onto a cutting board; cut into bite-size squares.