Spatchcock the chicken by removing the backbone.
In a large bowl, mix lemon juice, zest, garlic, rosemary, olive oil, and salt.
Pat the chicken dry and add it to the marinade, breast side down.
Cover and refrigerate for 2-24 hours, flipping at least once.
30-60 minutes before cooking, remove the chicken from the fridge.
Scrape off excess marinade, drizzle with olive oil, and sprinkle with salt.
Preheat the grill on high heat for at least 5 minutes.
Place the chicken breast side down on one burner and turn the heat under the chicken down to low, keeping the other burner on high.
Place a cast iron pan over the chicken and cook for 15 minutes.
Flip the chicken and cook for another 15 minutes over low heat.
Check the internal temperature; it should read 165 F.
If not, flip the chicken every 7-8 minutes until cooked, around 45 minutes total.
Let the chicken rest on fennel tops for 15 minutes before serving with lemon wedges.
