Adjust the oven rack to the lowest position and preheat the oven to CONVECTION/ROAST 375°F. Rub the oil all over the chicken, followed by the garlic powder. Season generously with salt and pepper. Place the chicken in a 9-by-13-inch baking dish or rimmed sheet pan. Stuff the chicken’s cavity with 1 lemon half and the parsley sprigs. Tuck the wings under the chicken and use butcher’s twine to tie the bony ends of the legs together.
Insert the temperature probe into the thickest part of the chicken between the leg and the thigh. Scatter the garlic around the chicken and place the remaining 3 lemon halves cut side down in the pan. Pour in ½ cup water around (but not over) the chicken.
Place the chicken in the oven and insert the probe’s plug into the probe jack. Set the probe temperature for 170°F, and roast until the probe temperature chime sounds, about 1 hour.
Remove the chicken from the oven and remove the probe. Lift the chicken and tilt it over the pan to pour off any juices that collected in the cavity, then transfer the chicken to a cutting board and loosely tent with foil for 10 minutes. Remove the parsley from the cavity and discard. Transfer the roasted lemons from the roasting pan and the cavity to a fine-mesh sieve set over the baking dish. Mash down on the lemons to extract their juices; discard the lemons. Use a fork to smash the garlic cloves into the pan juices, taste, and add more salt or pepper if needed. Transfer the pan juices to a gravy dish, carve the chicken, and serve with the pan gravy.
Variation: Honey-Thyme Glaze
Omit the lemons and garlic. Set the probe temperature for 150°F and roast the chicken until the temperature chime sounds, about 40 minutes. About 40 minutes after the chicken goes into the oven, make the honey thyme glaze: Heat ½ cup honey and 1 teaspoon chopped fresh thyme leaves in a small saucepan over medium-low heat. Turn off the heat and cover the pan to keep the honey warm. Use several fresh thyme sprigs to brush the warm honey mixture over the chicken and reset the probe temperature for 170°F. Baste the chicken every 10 minutes with the warm honey mixture until the probe temperature chime sounds, about 20 minutes longer. Proceed with the recipe as instructed, serving the pan juices alongside the chicken.
Variation: Smoked Paprika and Garlic
Substitute 2 navel oranges for the lemons. Rub the chicken with 2 tablespoons smoked paprika along with the garlic powder. Proceed with the recipe as instructed.