Preheat your oven to 350°F (175°C).

In a medium bowl, combine the rolled oats, gluten-free flour, baking powder, baking soda, salt, and ground cinnamon. Stir until well mixed.

In a large bowl, cream together the softened unsalted butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes.

Add the eggs and vanilla extract to the butter and sugar mixture, beating in the eggs one at a time.

Gradually add the dry ingredients to the wet mixture and mix until just combined. Fold in raisins if using.

Drop rounded tablespoons of dough onto a prepared baking sheet, spacing them about 2 inches apart.

Bake for 10-12 minutes until edges are lightly golden and centers remain soft. Cool on the baking sheet for 5 minutes before transferring to a wire rack.

Prepare the icing by whisking together powdered sugar, milk, and vanilla extract until smooth.

Once cookies are cool, drizzle icing over the top and let set before serving.