Pat chicken dry with paper towels. Place breast-side down on a cutting board and use kitchen shears to cut along both sides of the backbone, removing it completely. Flip chicken over and press firmly on the breastbone until it cracks and lays flat.
In a small bowl, combine olive oil, lemon juice, lemon zest, minced garlic, rosemary, thyme, oregano, salt, black pepper, smoked paprika, and onion powder. Whisk until well combined.
Loosen the skin from the chicken breast and thighs by sliding your fingers underneath. Rub one-third of marinade under the skin, another third on the skin surface, and remaining marinade on the underside. Refrigerate for 2-4 hours or overnight, then bring to room temperature 30 minutes before grilling.
Preheat grill to 375-400°F. For gas grill, turn off burners on one side. For charcoal, push coals to one side. Place a drip pan with water on the unheated side and lightly oil the grill grates.
Place chicken skin-side up on the indirect heat side of the grill. Close lid and cook for 20 minutes, then rotate 180 degrees. Continue cooking with lid closed for another 20-25 minutes until internal temperature reaches 165°F in the thickest part of the thigh.
Remove chicken from grill using tongs and transfer to a cutting board. Tent loosely with foil and rest for 10-15 minutes. Carve into pieces and serve immediately.