Preheat your oven to 350°F (175°C). Grease the baking pan or line it with parchment paper for easy removal of the bars.
In a medium bowl, whisk together the rolled oats, all-purpose flour, baking soda, salt, and ground cinnamon. Set aside.
In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until smooth and creamy.
Add the egg and vanilla extract to the butter mixture and mix until well combined.
Gradually add the dry oat mixture to the wet mixture, stirring until just combined.
Fold in the raisins until they are evenly distributed throughout the batter.
Spread the batter evenly into the prepared baking pan, smoothing the top with a spatula.
Bake in the preheated oven for about 25 minutes, or until the edges are golden and a toothpick inserted in the center comes out clean.
Allow the cookie bars to cool in the pan for at least 10 minutes before slicing into squares or rectangles.