Line a 9x9 inch baking pan with parchment paper to prevent sticking.
In a saucepan over medium heat, melt the butter until just bubbling and fragrant, about 2-3 minutes.
Pour the melted butter into a mixing bowl, then add the oats, brown sugar, cinnamon, and salt.
Stir the mixture thoroughly with a spatula until all oats are coated and the mixture is crumbly but sticky when pressed.
Transfer the mixture into the prepared pan and press down firmly with the back of a spatula or your fingers to create an even, compact layer.
Bake in a preheated oven at 180°C (350°F) for 15-20 minutes, until the edges are golden and fragrant.
Remove the pan from the oven and let the bars cool in the pan for at least 20 minutes, allowing them to firm up.
Once cooled, lift the bars out using the parchment paper and transfer to a cutting board.
Use a sharp knife to cut into 8-12 rectangles, wiping the blade with a damp cloth between slices for clean edges.
Serve the bars warm or at room temperature, storing any leftovers in an airtight container for up to three days.
