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 creamy.
Add the eggs one at a time, beating 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, pressing gently to smooth the surface.
Bake for 22 to 25 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with a few moist crumbs.
Remove from the oven and allow the bars to cool completely in the pan on a wire rack before cutting into 16 squares.
Serve and enjoy your chocolate chip oatmeal cookie bars!