Sauté onion, carrots, and celery in olive oil for 5-7 minutes.
Add garlic and diced chicken; season with oregano, salt, and pepper.
Pour in broth and bring to a gentle boil.
Reduce heat, cover, and simmer for 10 minutes.
Add orzo (or rice) and simmer until tender (8-10 mins for orzo).
Remove from heat and stir in lemon juice and lemon zest.
Fold in fresh dill and parsley.
Taste for seasoning and serve warm.