Canny Cannelloni

• 16 cannelioni tubes
• 1 onion (finely chopped)
• 1 pesto
• 300 ml skimmed milk
• 130 gr pink alaska salmon (canned)
• 50 gr breadcrumbs (fresh)
• 36 gr button mushrooms (chopped)
• 34 gr parmesan cheese
• 24 gr butter
• 14 gr flour (plain)