Start by cooking the pasta until al dente. Fry the onions in a pan with
Then prepare the béchamel sauce. Melt the butter in a pot and then add the flour all at once. Cook the butter and flour together for a few minutes and then add the milk, salt and pepper. Turn the heat down slightly and whisk the mixture continuously until the sauce thickens and you can no longer taste the flour.
At this stage you can combine the pasta with the béchamel sauce, chicken and vegetables, and adjust the seasoning if necessary. Transfer the mixture to an ovenproof dish, sprinkle with the grated mozzarella and then add the fresh origanum leaves.