Rinse the barley and boil in plenty of water until tender. In the meantime, gently fry the onion in the butter until soft; add the peas and the finely diced carrots and zucchini. Season with salt and pepper, sprinkle with a little water and cook for approx 10 minutes. Mix the vegetables with the drained but still warm barley. Add the eggs, cheeses and the nutmeg. Season with salt if necessary.
Beat the egg white with a pinch of salt, until stiff and fold into the mixture, then pour into a greased loaf tin lined with oven paper. Cover with aluminium foil and bake in a pre-heated oven at 180C – Gas 4, for 45 minutes. Remove the foil and cook for another 20 minutes.
Slice the mould, serve with a simple tomato sauce.