In a large pot of salted boiling water cook pasta until al dente; drain immediately. Keep pasta warm.
Meanwhile in a medium saucepan on high heat combine the cup of water, vegetable stock cube, tarragon, chilli flakes and oregano. Bring the mixture to a boil and add the Brussels sprouts, green beans, potatoes, carrots and onion. Turn the stove down to medium heat and let the vegetables cook until tender.
Stir the 2 tablespoons of water into the vegetable mixture and add the sour cream and the flour or cornflour. Stir well and cook until thickened and bubbly. Serve the vegetable mixture over the warm spaghetti and top with Parmesan cheese. Season with salt and pepper to taste.