Preheat the oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment paper.
Heat butter in a microwave-safe bowl in the microwave until melted.
Add sugar and stir to combine. Add beaten egg and mix well. Stir in oats, flour, vanilla, salt, and baking powder.
Drop spoonfuls of dough 3 inches apart onto the prepared baking sheet as the dough will spread.
Bake in the preheated oven until edges are golden brown, about 8 minutes.
Let cool completely before removing cookies from the foil.
