Set oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a bowl, whisk oats, flour, baking soda, cinnamon, and salt.
In a separate bowl, beat butter, brown sugar, and white sugar until fluffy. Add egg and vanilla; mix well.
Gradually add dry ingredients to the wet. Stir in cranberries and pistachios.
Drop tablespoon-sized scoops onto the baking sheet, spacing them 2 inches apart. Bake for 10–12 minutes, or until golden at the edges.
Let cookies cool on the sheet for 5 minutes, then transfer to a wire rack. Store in an airtight container for up to a week.