Preheat the oven to 200C/180C Fan/Gas 6. Line an 8" square baking tin.
In a large bowl, combine the oats, peanut butter and brown sugar. Beat together for a few minutes until entirely combined.
Add in the flour, baking soda, chocolate and a pinch of salt and bring together into a cookie-dough like texture.
Press this into the lined tin (I use my hands to press it out evenly). Bake for about 20 minutes until golden brown on top.
Let cool on a wire rack before slicing!