Preheat the oven to 425 degrees F. Coat a large rimmed baking sheet with nonstick cooking spray.
Pat the chicken dry with a paper towel. Using a sharp knife, score the chicken breast in a grid pattern, making sure you don't cut all the way through (slice across width 5 to 6 times then rotate the chicken and slice lengthwise to create a cross-hatch pattern). Place the pieces of chicken on the prepared baking sheet.
Place the potatoes, zucchini, tomatoes, and onion in a large bowl and toss with 2 tablespoons olive oil, garlic powder, ½ teaspoon salt, and pepper, to taste. Spread the potatoes and veggies around the chicken.
In the empty veggie bowl, mix together the feta, remaining ¼ cup olive oil, the juice from 1 lemon, parsley, garlic, oregano, thyme, remaining ½ teaspoon salt, and pepper, to taste. Spread the feta mixture over each piece of chicken. Slice the remaining lemon in half and tuck the two halves, cut side up, on the baking sheet between some of the veggies.
Roast for 35 to 40 minutes or until the chicken has reached an internal temperature of 165 degrees F. Set the oven to BROIL and cook for an additional 3 to 4 minutes, to form a nice golden brown crust on the cheese mixture.
Remove from the oven. If there is a lot of excess liquid on the baking sheet, you can pour or spoon it off (drizzle a little over the chicken, if desired). When the lemons are cool enough to handle, squeeze the juice over everything and serve.