Preheat oven to 350 degrees F. Line a 13x9x2-inch baking pan with foil, extending foil over the edges of the pan. Grease foil; set pan aside.
In a large mixing bowl stir together flour, brown sugar, and cinnamon. Add butter and vanilla. Beat with an electric mixer on low speed until mixture resembles coarse crumbs. Stir in pecans and 1/2 cup of the milk chocolate pieces. Press mixture evenly into the bottom of the prepared pan.
Bake for 25 to 30 minutes or until golden brown. Sprinkle bars with the remaining 1/2 cup milk chocolate pieces; let stand on a wire rack for 5 minutes to soften. Using a table knife, swirl the chocolate pieces and spread a thin layer of chocolate over the bars. Immediately sprinkle with the toffee pieces. Cool completely in pan on a wire rack. Use foil to lift uncut bars out of pan. Cut into bars.