To poach the chicken, place chicken, onion, lemon, carrot, celery, bay and herb bundle in a pot, cover chicken with water and bring to boil. Once boiling, reduce heat and simmer 45 minutes. Strain and reserve poaching liquids, cool chicken to handle. Remove skin and bones then pull meat into thin, bite-sized pieces.
For the pasta, heat EVOO, 1 turn of the pan, with butter over medium heat. Add carrots, zucchini, leeks and garlic, season with salt and white pepper, and saut to tender, 6-7 minutes. Sprinkle veggies with flour and stir a minute more. Deglaze pan with wine then stir in 2 cups reserved poaching liquid. Thicken to lightly coat spoon, add in chicken and peas, and reduce heat to low.
Bring a pot of water to a boil for pasta. Add salt and cook pasta to al dente. Drain and toss with chicken and sauce, adding an additional 1/2 cup poaching liquid if pasta gets too tight.
Zest lemon and combine with finely chopped herbs. Juice lemon into pasta and serve in shallow bowls topped with gremolata and some cheese.