Make the marinade in a large bowl by combining the avocado oil, lemon zest, rosemary, garlic, kosher salt and black pepper. Stir this rosemary lemon chicken marinade with a fork to combine.
1/4 cup avocado oil, 3 lemons, 3 sprigs of rosemary, 2 cloves of garlic, 3 teaspoons kosher salt, 2 teaspoons black pepper
Spatchcock the chicken by placing the whole chicken breast side down on your cutting board. Using kitchen shears, cut along either side of the spine to remove the spine from the chicken. Flip the chicken over so it is now breast side up, place your palm on the breast bone in the center, then use medium pressure to push down on the breast until you hear a crack and are able to get the chicken flattened. 1 whole chicken (around 3 pounds)
Marinate the chicken by placing the butterflied chicken in the large bowl with the marinade. Use your hands to rub it all over the chicken on both sides. You can grill right away, or allow the chicken to marinate for up to 3 days covered in the refrigerator.
Heat your grill over medium heat (I heat my Traeger Grill at 400ºF). Clean and oil the grill grates.
Grill the chicken and lemons on your grill once your grill is fully heated. Grill the chicken breast side up, and the lemons cut side down. Cook until the chicken skin is crispy and the chicken has an internal temperature of 165ºF. On my Traeger Grill it takes about 45-55 minutes. No need to flip the chicken, but you can flip it half way through cooking if you prefer.
Rest the chicken on your cutting board for 10 minutes.
Carve and serve the chicken along with the grilled lemons. Squeeze out the grilled lemons on top of the chicken. The lemon pulp gets thick and concentrated as it is grilled and loses a lot of its sourness. It's very delicious!
Leftover grilled spatchcocked chicken will keep in an airtight container refrigerated for at least 5 days, or frozen for at least 6 months.
See the Recipe Notes below for more tips, FAQ's and ingredient substitutions.