Preheat the oven to 350°F (175°C). Line a large baking sheet with parchment paper.
In a large bowl, cream together the softened butter, light brown sugar, and granulated sugar until light and fluffy, about 3 minutes.
Beat in the eggs one at a time, mixing well after each addition, then 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 throughout the dough.
Divide the dough into 6 equal portions and shape each into a large ball. Place them spaced apart on the prepared baking sheet, then gently flatten each ball to about 3/4 inch thickness.
Bake in the preheated oven for 18 to 20 minutes, or until the edges are golden brown and the centers look set but still soft.
Remove the cookies from the oven and allow them to cool on the baking sheet for 10 minutes before transferring to a wire rack to cool completely.