Combine the lemon, parsley, garlic, oil and salt in a blender until mostly smooth.
Toss the chicken with the gremolata and marinate overnight or for at least 4 hours.
Preheat the oven to 350°F.
Remove the chicken from the marinade, discard marinade and season chicken with salt and pepper. Roast on a baking sheet until cooked through, about 22-28 minutes.
Toss the mushrooms with 1 tablespoon olive oil and a pinch of salt on a baking sheet. Roast for 10-12 minutes, until crisp.
Melt the butter and remaining oil in a large skillet.
Sauté the onion, celery and garlic until soft, about 7-10 minutes. Add the wine, chicken broth, and roasted mushrooms and bring to boil. Add the cooked farro and simmer for 20 to 30 minutes. Stir in the cheese and season with salt and pepper.
Cool slightly, then fold in the peas and parsley.
Combine all of the pesto ingredients in a blender or food processor until smooth. Season to taste.
To serve, divide the risotto between plates, top with gremolata chicken and drizzle with arugula pesto. Sprinkle with cheese.