Heat oil in Dutch oven or heavy stockpot over medium heat. Add onion, celery and carrots. Cook until the onions and celery are soft; approximately 6-7 minutes. Reduce heat to low. Add garlic, marjoram, thyme, and rosemary; cook for 1 minute stirring constantly.
Raise heat to medium low. Sprinkle flour over vegetables; cook for 2-3 minutes stirring constantly. Slowly stir in chicken broth. Add bay leaves and bring the soup to a boil; stirring several times.
Reduce the heat to a simmer. Add the orzo and chicken and cook until the orzo is tender; 8-10 minutes. Stir in lemon juice and spinach cooking until the spinach is wilted.
Season with kosher salt and fresh ground black pepper to taste. Remove bay leaves. For best results serve promptly.
