Add the tomato paste and cook stirring constantly for 2-3 min. Add the tinned tomatoes and stock, bring to a gentle simmer. Allow to simmer for 30 min until reduced and thickened. Taste for seasoning.
In a large pot of boiling salted water, boil the spaghetti according to package instructions. Once al dente, drain the pasta.
Divide the spaghetti between bowls and top with the mushroom bolognese. Sprinkle bowls with Parmesan cheese and fresh parsley.