Preheat the oven to 350°F. Grease an 8x8 inch baking pan.
In a saucepan, melt the butter over medium heat. Add brown sugar and stir until dissolved, 1-2 minutes. Set aside to cool slightly.
In a large bowl, mix together the oats, baking powder and salt.
Pour the butter mixture over the oat mixture and stir until fully blended.
Press the mixture firmly into the prepared baking pan.
Bake for 18-22 minutes until lightly browned. Cool completely before cutting into bars.