Preheat your oven to 350°F (175°C) for even baking.
In a large mixing bowl, cream together the shortening, brown sugar, and granulated sugar until light and fluffy.
Add the egg, water, and vanilla extract, mixing until well combined.
In a separate bowl, whisk together the flour, salt, and baking soda. Gradually add to the wet mixture, stirring until just combined.
Fold in the oats and Butterfinger bits until evenly distributed.
Drop rounded spoonfuls of dough onto a baking sheet lined with parchment paper, leaving about 2 inches between each cookie.
Bake for 10-12 minutes or until the edges are lightly golden. Allow to cool for 5 minutes before transferring to a wire rack.
Enjoy your Butterfinger Oatmeal Cookies warm or at room temperature!