Pre-heat the oven to 200C, 400F, gas mark 6. Place the potato cubes onto a non-stick baking tray and spray lightly with the rapeseed oil and place in the oven to bake.
After the potatoes have been in the oven for 10-12 minutes bring a large pan of water to the boil and add the stock cube and the spaghetti and cook for 10-12 minutes stirring occasionally.
1 minute before then end of the cooking of the spaghetti add the fresh spinach leaves, stir and cook for just 30-40 seconds more, Drain immediatly and transfer to a warmed pasta bowl.
Remove the roasted sweet potato from the oven and sprinkle over the spaghetti and spinach. Srinkle over the dried mixed herbs and the grated pecorino or parmesan. Serve straight away