In a dutch oven, over medium high heat. Heat olive oil and melt the butter.
Add onion, carrot and celery, and cook for 5 minutes.
Add garlic, and cook for 30 seconds.
Add flour, stir and cook for 1 minute.
Pour chicken stock, add the chicken breasts, bay leaf, and dried herbs.
Bring to a boil, then reduce the heat and simmer covered for 15 minutes.
Add the orzo and cook uncovered while stirring regularly for 10 minutes (you don’t want the orzo to stick to the bottom of the pot).
Remove from heat, discard bay leaf, take the chicken out (and make sure it reached 165°F/74°C) and shred it then return it.
Stir in the lemon juice, zest, and parsley, season with salt and pepper. Taste the soup and adjust seasonings to your preference.