Heat 1 tbsp olive oil in a large saucepan on high heat.

Add lamb and brown in batches; remove from pan.

Heat 1 tbsp olive oil in same pan. Add onions and coarsely chopped carrots and celery.

Cook until browned; return lamb to pan.

Add bay leaves, peppercorns, parsley sprigs, thyme, and 4 quarts water. Bring to a boil.

Reduce heat to low and simmer, uncovered, for 2 hours, skimming surface occasionally.

Strain stock through muslin-lined strainer into a large bowl, reserving lamb; discard vegetables.

Refrigerate stock for several hours or overnight. Discard solidified fat.

Pull meat off bones; reserve meat. Discard bones.

Heat remaining 2 tbsp olive oil in a clean saucepan on medium heat.

Add garlic and finely chopped carrots and celery. Cook until softened.

Add barley; stir to coat.

Add oregano and prepared lamb stock; bring to a boil.

Reduce heat to low; simmer, covered, for 30 mins, or until barley is tender.

Blend or process 1/3 of the soup until pureed. Return pureed soup to pan.

Add reserved lamb meat; simmer, covered, for 5 mins, or until meat is heated through.

Just before serving, stir in chopped parsley and lemon juice to taste.