Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking pan or line it with parchment paper.
In a large mixing bowl, combine the melted butter, light brown sugar, and granulated sugar. Stir until smooth and well combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the rolled oats and semisweet chocolate chips until evenly distributed.
Spread the batter evenly into the prepared baking pan and smooth the top with a spatula.
Bake in the preheated oven for 22 to 25 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out clean or with a few moist crumbs.
Remove from the oven and allow to cool completely in the pan on a wire rack before cutting into 16 bars.