Preheat the grill to medium heat, about 350°F. Set it up for indirect grilling, with one side hotter and one side cooler.
Pat the chicken very dry with paper towels. Rub all over with olive oil, then season both sides with salt, pepper, garlic powder, and paprika.
Make the chimichurri butter. In a small bowl, mix the Challenge Salted Butter, parsley, cilantro if using, garlic, red wine vinegar, lemon zest, lemon juice, fresh oregano, red pepper flakes, and black pepper until combined.
Place the chicken skin-side up on the cooler side of the grill. Close the lid and cook for 25–35 minutes, rotating the chicken occasionally, until it is mostly cooked through.
Brush the chicken with some of the chimichurri butter. Continue grilling for 10–15 minutes more, brushing once or twice with more butter, until the skin is golden and the thickest part of the breast reaches 165°F and the thighs reach 175°F.
If you want extra color, move the chicken skin-side down over the hotter side of the grill for 1–2 minutes at the end. Watch closely so the butter and herbs do not burn.
Transfer the chicken to a cutting board and let it rest for 10 minutes.
Carve the chicken and serve with the remaining chimichurri butter spooned over the top.
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