Preheat oven to 400°F with a rack positioned one notch up from the center. Or, prepare a grill with two-zones: direct, medium-high heat and indirect heat. 

To spatchcock a chicken, place it breast-side down on a cutting board. Using kitchen scissors or poultry shears, cut along each side of the backbone. Flip the bird over and spread it out, pressing down and cracking the breastbone so that the bird lies flat. Cut the wing tips off and save them and the backbone for stock.

Salt chickens on both sides with Kosher salt and refrigerate uncovered overnight or for a minimum of 1 hour.

Place garlic in a small pot and cover with EVOO. Heat gently and let bubble 3-5 minutes. Drop in the rosemary bundle then brush the birds all over with garlic oil using the rosemary as a brush. Season the chicken with pepper and chopped rosemary.

Arrange the chicken on a wire rack set onto a large baking sheet and roast 45-60 minutes to an internal temperature of 165°F. Or, grill chicken breast-side down over direct heat to brown, about 5 minutes, then turn over and move to indirect heat. Cover and cook about 45 minutes, basting chicken occasionally with the garlic oil and rosemary brush until it reaches 165°F. During the last few minutes of cooking, grill or roast lemon halves.

Let chicken stand 10 minutes before carving. While they rest, make the Parsley Chimichurri: In a food processor bowl, combine parsley, lemon zest and juice, shallot, garlic, a fat pinch of salt and pulse to chop. Stream in oil to form sauce, transfer to a small bowl and stir in chili peppers to taste.

Douse chicken with charred or roasted lemon juice and serve topped with chimichurri, with extra sauce at the table.