Marinate chicken in the Italian dressing overnight in the refrigerator if possible. If you don't have time to marinate, just coat the chicken in the dressing and set aside (but you'll get more flavor if it does marinate).
Preheat oven to 400° (or 375° for convection).
Cut potatoes in half. Place into a bowl with the green beans.
Drizzle with olive oil. Sprinkle with salt and pepper. Add garlic powder.
Squeeze lemon juice into the bowl, and save the lemons.
Toss potatoes and green beans to coat with all of the ingredients.