Preheat oven to 325 degrees F.
Line a sheet pan with foil and place chicken thighs on it. Brush with oil. Season with some celery salt and fresh ground pepper. Bake for 30 minutes, Remove from the oven and left cool. Cut into a dice and set aside.
In a large stockpot, heat about 6 cups water to boiling. Add orzo and cook until al dente or about 10 minutes. Drain and lay out on a tray or sheet pan to cool. Drizzle with some olive oil and mix in, so the orzo doesn't stick together.
In the same stockpot that you made the orzo in, heat remaining tablespoon or so oil over medium heat, and add the fennel, carrots and celery. Saute until the vegetables are soften, about 5-6 minutes.
Add the leeks and garlic and cook until leeks are translucent or begin to soften.
Add the chicken stock and bring to a simmer. Simmer for about 10 minutes.
Add the diced chicken meat and orzo, and return to simmer. Simmer for about 5 minutes.
Add in parsley, salt and pepper to taste.
Add the spinach or other soup greens and simmer until cooked.