Heat the oven to 400℉. Grease a large, rimmed sheet pan with oil spray or a little oil.
Make the marinade: mix the lemon zest, lemon juice, olive oil, garlic, salt, herbs, pepper, and 2 tablespoons of parmesan in a small bowl.
Add the broccoli florets and gnocchi to a large bowl. Separate any gnocchi that may be stuck together. Whisk the marinade again then pour about half of it over the broccoli and gnocchi. Toss to coat.
Spread the broccoli and gnocchi out evenly on the prepared sheet pan. Place in the oven and roast for 10 minutes.
Meanwhile, add the chicken to the now empty bowl, pour over the remaining marinade and toss to coat.
Once the broccoli and gnocchi have cooked for 10 minutes, take the pan out of the oven, and push the broccoli and gnocchi to the edges of the pan to make room for the chicken in the center. Place the chicken pieces on the pan in a single layer.
Place the sheet pan back in the oven and cook until the chicken reaches an internal temp of 165℉, 15 to 20 minutes.
Sprinkle the remaining 2 tablespoons of parmesan cheese over the dish then serve with additional lemon slices, if desired.
