Place the butter in a pot and begin to melt. Once it's liquid add the sugar and stir until it's dissolved.
Take off the heat and use your danish dough whisk (or wooden spoon) to add the flour, baking powder, rolled oats, salt, and ginger.
Press the mixture into the prepared tin. Use the a clean wet hand or the back of a spoon to press all the mixture into the corners, and make an even surface.
Bake the slice for 15 minutes (or until golden brown).
While the slice is baking, wash the pot so you can use it to prepare the icing.