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 immediately and stir in the dried mixed herbs, season with the black pepper and transfer to a warmed pasta bowl.
Remove the roasted sweet potato from the oven and sprinkle over the top of the spaghetti and spinach. Top with the grated vegan pecorino. Serve straight away