Greek lamb with orzo

INGREDIENTS

• 1kg shoulder of lamb
• 2 onions , sliced
• 1 tbsp chopped oregano , or 1 tsp dried
• ½ tsp ground cinnamon
• 2 cinnamon sticks , broken in half
• 2 tbsp olive oil
• 400g can chopped tomatoes
• 1.2l hot chicken or vegetable stock
• 400g orzo (see know-how below)
• freshly grated parmesan , to serve