Preheat the oven to 180c/160c fan/350f/gas mark 4. If you are using an air fryer you only need to preheat it for a couple of minutes before baking at the same temperature.
Add flour, oats, brown sugar, cinnamon and salt to a large mixing bowl and mix well to combine.
Add the butter and rub in with your fingertips until you have a breadcrumb like texture.
Unroll the pastry (or roll our your block of pastry into a rectangle).
Spread with the apple sauce, leaving a border clear at the top and bottom of it landscape (lengthways).
Sprinkle the crumble over the apple sauce.
Roll the long side from the bottom to the top, rubbing a little water along the top border to help it seal. You will be left with a long sausage shape.
Cut slices of the pastry about 1 cm thick, a little thicker is ok.
Place the swirls on non-stick baking paper, leaving a space between them. If you are baking in an air fryer with shelves, if they are mesh, you can coat with a little spray oil to avoid sticking and place directly onto the mesh shelves.
Preheat your air fryer for a couple of minutes to 180c or 350f, if you are baking in an air fryer.
Bake the Danish pastry swirls for 15 to 20 minutes. If you are baking on baking paper, you might want to turn them once the top is golden, then give the other side a bake for a few minutes. If they are straight onto a mesh shelf, you may not need to turn them.
Leave them to cool completely until cool, then make the icing sugar.
Mix the icing sugar with the water until you have a thick icing, then drizzle over the cooled pastries.
Enjoy!