Preheat your oven to 350F (180C).
Spray a 13x9x2 inch baking dish with non-stick cooking spray. Line with parchment paper to fully cover the bottom of the dish and overhang along two sides. Set the pan aside.
In a large mixing bowl, stir together the flour, brown sugar and cinnamon. Try to break down any lumps of brown sugar.
Add in the melted butter and vanilla and mix with a wooden spoon until everything comes together and resembles course crumbs. Next, stir in ½ cup of the chocolate chips and the walnut pieces.
Tip the contents into your prepared pan and lightly press the mixture into the pan.
Place the pan in the middle rack of the oven and bake for 25 - 30 minutes until the cookie bar starts to turn lightly golden on top.
Bring the pan out of the oven and immediately, while the cookie bars are still hot, sprinkle the rest of the chocolate chips over the top and let stand for 2 minutes. The chocolate will melt from the heat of the cookie. After a couple minutes, use a palette knife or a small spatula to spread the chocolate over the top of the bars. Sprinkle the toffee bits all over the melted chocolate.
Let the bars cool on a wire rack until the chocolate is set. Remove the bars from the pan by using the edges of the overhanging parchment to lift the bars straight out onto a cutting board. Cut your bars into 16 pieces and enjoy!