Preheat oven to 350 degrees. Use ungreased cookie sheets or line cookie sheets with silicone baking mats.
Use electric mixer to beat shortening and butter until well incorporated. Add salt, sugar, and light brown sugar. Beat until lightened and fluffy.
On low speed, mix in egg and vanilla extract, scraping down sides as needed.
In a small bowl, whisk together flour, cornstarch, baking soda, baking powder, cinnamon, and oats. Gradually beat into butter mixture, about 1/2 cup at a time.
Stir in chocolate chunks.
Form dough into about 1 inch round balls and space 2 inches apart on cookie sheet. Bake until golden brown, 8-9 minutes.