Preheat your oven to 425°F (220°C).

Place the chicken breast-side down on a cutting board. Cut along both sides of the backbone using kitchen shears and remove it. Save the backbone for stock if you like.

Turn the chicken breast-side up. Press firmly on the breastbone until it cracks and the chicken lays flat.

Pat the chicken completely dry with paper towels. This is the most important step for crisp skin.

In a small bowl, combine 1 teaspoon salt, black pepper, paprika, garlic powder, and onion powder.

Drizzle the chicken with 2 tablespoons of olive oil on both sides. Season the chicken evenly on all sides: start with the back, flip, and finish with the breast.

Arrange the onion slices in the center of the pan, creating a bed for the chicken. The onions will lift the chicken slightly off the bottom of the pan, allowing hot air to circulate underneath. Place the spatchcocked chicken skin-side up directly on the onions.

Add the vegetables to the prepared roasting pan, drizzle oil over them and combine. Also season them with the remaining seasoning mix.

Roast them all for 50 to 60 minutes total until the chicken is fully cooked. The chicken breast should reach 165°F, and the chicken thigh should reach 175°F (check the thickest part of the thigh without touching bone). The chicken skin should be deep golden and crispy.

Remove the pan from the oven and transfer the chicken to a clean cutting board and tent it loosely with foil. Let it rest for 10 minutes before carving. Doing this keeps the meat moist and allows juices to redistribute throughout the meat.

While the chicken rests, keep the roasting pan in a warm spot. Spoon the pan juices over the vegetables to coat them.

Carve the chicken and serve the pieces with the roasted vegetables. Feel free to garnish the food with fresh parsley and serve it with lemon wedges on the side.