Chop chicken and set aside. Dice onion, peel and slice carrots and chop celery. Zest one lemon and juice it. Slice the other lemon and set aside.
In a large Dutch oven or soup pot add the olive oil over medium heat. Add the onion and sauté for 3 minutes. Add the carrot and celery, stirring and cooking for 4 minutes.
Add the salt, pepper and sprinkle the flour over all. Stir to mix in and cook flour, 3 minutes.
Carefully pour in wine and scrape up bits from bottom of pot. Add chicken, chicken broth, oregano, lemon zest and juice and orzo pasta, stirring to combine. Bring to a boil, lower the heat to low and simmer, stirring often for 20 minutes.
Serve each bowl topped with crumbled feta cheese, chopped parsley and sliced lemons.
Notes
I use my leftover Baked Greek Chicken, but rotisserie chicken or your own baked chicken works (white, dark or both).