Preheat oven to 350 degrees. Spray a 9×9 inch baking pan with nonstick spray.

In a large bowl, cream together the butter and brown sugar until fluffy. Add in the flour, baking powder and salt. Mix until everything comes together in a crumbly mixture. Mix in coconut and oats. The finished mixture will be dry and sandy. Press two cups of the mixture into the bottom of your prepared pan.

In a medium bowl, whisk together sweetened condensed milk, lime juice and zest. Pour over the top of the oat mixture in the pan. Crumble all the remaining oat mixture over the top of the lime filling and bake for 30 minutes until golden brown. Allow to cool completely before cutting. Keep in the fridge if you prefer them to be firmer.