Preheat your oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper, leaving some overhang for easy removal.
In a medium bowl, whisk together the flour, baking soda, salt, and ground cinnamon until well combined.
In a large mixing bowl, combine the melted butter, brown sugar, and granulated sugar. Mix until smooth and creamy.
Add the egg and vanilla extract to the butter and sugar mixture, stirring until fully incorporated.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Do not overmix.
Fold in the rolled oats, dried cranberries, chopped nuts, and chocolate chips until evenly distributed.
Spread the mixture evenly in the prepared baking pan, smoothing the top with a spatula.
Sprinkle the M&M-style candies on top for a pop of color and festive flair.
Bake in the preheated oven for 25-30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with a few moist crumbs.
Allow the bars to cool in the pan for about 10 minutes, then lift them out using the parchment overhang and transfer to a wire rack to cool completely before slicing into squares.