In two or three batches, brown lamb in a large saucepan. Turn the chunks of lamb over and brown all sides.
Add all the lamb back to the pot and stir in the onions, parsnips and carrots. Cook over medium heat for 3-4 minutes until vegetables begin to soften. Stir in the potatoes.
Add the oregano to the pot. Add rosemary, 1 cup of broth and 1 bottle of beer. Heat just to boiling and place the lid on tightly. Braise for 1 1/2 hours. Add the preserved lemon and braise for an additional hour.
Keep adding broth when needed, keeping the stew wet.
Combine the flour and butter in a small bowl. Mash together with the back of a fork to form a paste. Stir in the butter mixture until it dissolves in the stew and the stew thickens.
Add frozen peas and parsley and stir to combine. The heat from the stew will thaw the peas. Serve.