Preheat the oven to 350 F/ 180 C/ gas mark 4. Lightly grease a 23 cm/9'' pan and line with parchment paper. Set aside.
Whisk together the flour, baking powder, bicarbonate of soda, salt, pumpkin spice and cinnamon.
In another bowl beat together the eggs, oil and sugars for a few minutes until pale and fluffy.
Add the pumpkin puree and stir well to combine.
Gradually add the flour mixture stirring until the dry ingredients are no longer visible (use a whisk or spoon). Do not overstir.
Pour the batter into the pan and smooth out the top. Bake in the centre of the oven for 45 minutes (or until a toothpick inserted in the middle comes out clean).
Remove from the oven and set aside for 15 minutes then lift out of the pan and place on a rack to cool completely before decorating.
To make the cream cheese frosting beat together the ingredients for a couple of minutes until smooth and fluffy. Cover and refrigerate until you are ready to decorate the cake.
Notes
Use canned pumpkin puree, NOT homemade. Also make sure it's 100% pumpkin, not pumpkin pie filling.
Do NOT overstir the batter.
Cool the cake completely before decorating with the frosting.
You can make the cream cheese frosting ahead and keep refrigerated, covered for up to 2 days. Decorate the cake just before serving.
You can scatter more lemon zest over the top of the cake if you like (as in photos).