Carefully rinse the chicken with cold water. Squeeze lemon juice over the entire bird, then place the lemon halves inside the cavity of the chicken.
Take ¾ of the thyme sprigs and remove the thyme leaves from the stems by holding the top of the sprig and stripping the leaves downward. Sprinkle the thyme leaves all over the bird.
Next, sprinkle the sea salt, freshly cracked pepper, and garlic powder over the entire bird to taste.
Place the remaining thyme (including stems) inside the cavity of the chicken along with the garlic and onion.
Coat your roasting dish or large Dutch oven with olive oil cooking spray, then place the chicken on a rack inside the dish.
Put the meat thermometer into the thickest part of the thigh without touching the bone.
Roast uncovered for 3½-4 hours or until the thermometer reads 165-170 degrees. Side Note: I start basting the bird after 2 hours and repeat every ½ hour after that. For crispy skin, stop basting for the last hour of cooking.
Remove from the oven and let the bird "rest" for at least 10 minutes before carving. Serve and enjoy!