Preheat oven to 350°F. Line baking sheets with parchment paper or lightly grease them. Set aside.
In a large mixing bowl, beat shortening, granulated sugar, and brown sugar with an electric mixer or wooden spoon until light and fluffy (about 2-3 minutes).
Stir in hot water and vanilla extract until smooth.
In a small bowl, whisk together flour, baking soda, and salt.
Add dry ingredients to shortening mixture. Mix on low speed or by hand just until combined. Fold in oats with a spoon until evenly distributed. Dough will be thick.
Drop tablespoon-sized scoops of dough onto prepared baking sheets, spacing 2 inches apart. Flatten slightly with fingers. Bake 10-12 minutes until edges are golden brown and centers look set. Cookies will firm up as they cool.
Let cookies cool on baking sheet for 2 minutes. Transfer to a wire rack to cool completely.