Preheat the oven to 425°F (220°C) and lightly grease a large baking sheet or roasting pan.
Pat the chicken completely dry with paper towels.
In a small bowl, combine olive oil, melted butter, minced garlic, salt, pepper, paprika, thyme, rosemary, parsley, and onion powder.
Rub the seasoning mixture all over the chicken, including underneath the skin where possible.
Place the lemon halves inside the chicken cavity.
Toss the potatoes with any remaining seasoning mixture until evenly coated.
Arrange the potatoes around the chicken in a single layer.
Roast for 75–90 minutes, or until the thickest part of the chicken reaches 165°F (74°C) and the potatoes are golden and tender.
Stir the potatoes halfway through roasting for even browning.
Remove the pan from the oven and let the chicken rest for 10 minutes before carving.
Garnish with fresh parsley and serve with the roasted garlic potatoes.