Persian rhubarb, parsley and mint stew

Here I have a regional dish from mountainous parts of Iran. It is similar to celery stew but with out limes or lemons since rhubarb is very acidic.

200 gr Italian parsley with stems, finely chopped
100 gr mint,  finely chopped
400 gr rhubarb, finely chopped
1 medium onion, finely chopped, divided
500 gr lamb shanks(or beef ribs)
1 TSP turmeric
1/2 TSP ground cardamon
pinch of saffron
2 cups brown beef stock
Salt and pepper to season

Follow the instruction in Persian celery, parsley and mint stew. The only difference is in roasting half of the rhubarb and adding at the end and when plating.
Brush the pices with a mixture of oil and honey. In a pre-heated oven(max heat) bake for 10-15 minutes