Heat the oven to 200C (180C fan)/390F/gas 6, and grease and line a 1kg loaf tin with baking paper.
Put the flour, bicarb, baking powder, spices, sugar and chocolate in a large bowl and mix well.
In a second bowl, combine the pumpkin puree, oil and milk.
Fold the wet ingredients into the dry until well combined, then put to one side.
Next, make the crumble topping by mixing the sugar, pecans, flour and oil in a small bowl.
Transfer the cake batter to the lined loaf tin, smooth out the top with the back of a spoon, then tap the tin on the countertop to knock out any bubbles.
Top evenly with the crumble mixture, then bake for 55 minutes, or until a skewer inserted into the centre comes out clean; don’t worry if it has melted chocolate on it.
Take out of the oven, leave the cake to cool in its tin, then lift out, slice and serve.
