Dried herbs and a simple creamy sauce give this classic meal a refined feel. Smarts: Feel free to use any type of tomatoes to roast with the zucchini. Cherry, plum, or Roma tomatoes would all be great.
Spread zucchini and tomatoes out on a sheet pan. Toss with balsamic vinegar (portion for vegetables), olive oil (portion for vegetables), Italian seasoning (portion for vegetables), and some salt and pepper. Transfer vegetables to the oven and roast until tender, shaking the pan halfway through cooking, ~25 minutes total.
Once vegetables are roasting, heat an oven-safe skillet with cooking oil over medium-high heat. Add chicken and sear on both sides until golden brown but not cooked through, 6 to 7 minutes total. Add stock and cover skillet with foil. Transfer skillet to oven and continue roasting chicken for 8 to 12 minutes more (depending on thickness; chicken is done when it reaches 165F / 74C).
When chicken is done, transfer to a cutting board, cover, and let rest for at least 5 minutes.
While chicken rests, combine balsamic vinegar, lemon juice, and olive oil (portions for salad). Toss with arugula, avocados, and sunflower seeds.
Slice chicken and serve over vegetables with sauce on top. Enjoy salad on the side.