Heat the oil in a large frying pan and fry the onion, garlic and squash for 5 minutes. Stir in the walnuts and mushrooms and cook for 3 minutes.
Add the orzo and stock, cover the pan and simmer for 10 minutes, stirring occasionally until the pasta is tender. Season and stir in the vinegar and parsley to serve.
Cooks tip
Try adding some blue cheese at the end of cooking or sprinkle with Parmesan for a non-plant based option.