Preheat the oven to 180°C and grease an 8 inch/20cm springform cake tin.
In a mixing bowl, combine the self-raising flour, caster sugar and salt.
Add the butter and rub it into the flour with your fingers until it resembles damp sand or breadcrumbs.
Stir in the oat milk. The dough should come together in a soft clump. Dust with a little flour and knead for 2-3 minutes so it holds its shape.
Dust your work surface and roll out the dough into a rectangle approximately 60cm x 30cm. The dough should be soft but hold its shape.
Melt the butter for the cinnamon filling and mix in the pumpkin purée. In a separate bowl, combine the spices and sugar.
Spread the melted butter and pumpkin mixture evenly over the dough, then sprinkle over the spiced sugar.
Cut the dough into strips about 3cm wide. Starting at the long edge of each strip, roll it tightly into a log.
Place the first log in the centre of the greased springform tin. Roll the remaining strips around it until all strips are used, forming one giant cinnamon swirl.
Bake in the preheated oven at 180°C for 25 minutes, then reduce the heat to 160°C, cover with foil and bake for a further 35 minutes. Remove from the oven and leave to cool for 20 minutes.
While the cake is baking, make the icing by placing the cream cheese in a bowl with the icing sugar, vanilla and oat milk. Stir with a fork until smooth and creamy.
Drizzle the icing over the cooled giant cinnamon swirl before serving.