Preheat the oven to 170°C/fan oven 150°C/Gas Mark 3. Grease a 20cm (8in) round cake tin with a little Trex, then line with baking paper.
Put the Trex, sugar, eggs, vanilla and orange zest into a large mixing bowl. Sift in the flour, salt, baking powder, bicarbonate of soda and cinnamon. Use a wooden spoon to beat together until smooth and creamy, about one to two minutes.
Add the grated carrot, almonds and raisins and fold them in with a large metal spoon. Transfer to the prepared tin and level the surface.
Bake on the middle shelf of the oven for one hour, or until a fine skewer inserted into the centre of the cake comes out clean. Cool in the tin for 10 minutes, then transfer to a wire rack to cool completely.
To make the frosting, beat the cream cheese and sugar together. Spread over the top of the cake and sprinkle with orange zest and pomegranate seeds.