Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a medium bowl, combine the rolled oats, all-purpose flour, baking soda, ground cinnamon, and salt. Mix well and set aside.
In a large bowl, whisk together the melted unsalted butter, brown sugar, and granulated sugar until smooth.
Add the egg and vanilla extract to the butter and sugar mixture and whisk until fully combined.
Gradually add the dry oat mixture to the wet ingredients, stirring until just combined.
Fold in the raisins evenly throughout the dough.
Drop rounded tablespoons of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 18 to 20 minutes, or until the edges are golden brown and the centers are set.
Remove the cookies from the oven and allow them to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.