Thinly slice the onion and the mushrooms.
Heat a spoonful of oil in a pan then add the onion. Sauté for 5 minutes, then add the mushrooms, chilli flakes, garlic and thyme leaves. Gently cook for 5 minutes, then add half oft the lemon juice and cook for a couple of minutes.
Meanwhile, grate the courgette and drain the beans. Add these to the mushrooms, season with salt and pepper. Add the other half of the lemon juice, then sauté, under cover, for 5 minutes.
Finally add the chopped parsley, then serve with a dah of cider vinegar.