Preheat oven to 325°F (160°C).

Cream together brown sugar, butter, and eggs until light and fluffy.

In a separate bowl, sift together flour, salt, and baking powder.

Gradually add the dry ingredients to the creamed mixture, mixing until just combined.

Stir in cinnamon and oatmeal until evenly distributed.

In a small bowl, dissolve soda in boiling water.

Add the soda mixture to the batter and mix well.

Drop spoonfuls of batter onto ungreased baking sheets.

Bake for 10 to 15 minutes, or until edges are lightly golden.

Let cool on baking sheets for a few minutes before transferring to a wire rack to cool completely.

Sandwich two cookies together with your favorite filling (e.g., buttercream, cream cheese frosting).