Cut the courgette into long, thin slices, using a vegetable peeler. Brush or spray them with a little oil, then fry them in a hot pan. Put them on a plate and rest.
Meanwhile, thinly slice the onion and cut the big mushrooms into smaller chunks.
In the same pan, heat some oil and sauté the onion for 5 minutes. Add the mushrooms, chilli flakes and garlic. Stir for a minute, then add the lemon juice. Put a lid on and gently sauté for about 10 minutes or until the mushrooms have softened.
Put back the courgette and add the balsamic vinegar. Turn the heat up and caramelise the vegetables a bit.
Season to taste and serve with fresh herbs scattered on top.