Heat grill to 400-degrees (you can do this in your oven, too, at the same temp.).
Season chicken with Greek seasoning and salt and pepper. Set aside.
Divide potatoes, zucchini, and tomatoes into 4-5 equal portions.
Evenly distribute vegetables between 4-5 12-18" foil squares.
Drizzle a little olive oil over each portion of vegetables and season with Greek seasoning and salt and pepper.
Place chicken over the top of each vegetable pile and drizzle with a little more olive oil.
Place a thin slice of lemon or two over each piece of chicken.
Tightly seal foil packets by folding up the sides over the contents and tightly folding up the ends over the seam.
Grill 40-45 minutes or until potatoes are tender and chicken is cooked through.
Be careful when opening packets. Steam will release and be VERY HOT.
Open packets and season with salt and pepper, if needed.
Sprinkle a little Feta cheese over each packet and serve with extra lemon slices.