Preheat oven to 375F. Line a baking sheet with parchment paper.
Add the flour, oats, sugar, baking soda and salt to a medium mixing bowl. Stir together.
Add the cold butter and combine it to the dry mixture, using a fork or your hands. You want to get a crumbly mixture.
Add the water and stir it all together until you get a slightly wet dough.
Sprinkle flour on a clean surface. Transfer the dough to the floured surface. Sprinkle a small amount of flour on the dough and roll out until you get a 1/2" thick rectangle. Cut into 12 squares and transfer to the baking sheet, placed close together (see pictures). Alternatively, you can do these steps directly on the prepared baking sheet.
Bake for 15 minutes or until lightly golden and crispy with a slightly soft middle.
Let them cool completely, then drizzle with melted chocolate if desired. Store in an airtight container at room temperature or in the freezer. They will be slightly crumbly, especially when warm.