Get the charcoal briquettes going in the Weber Rapid Fire Charcoal Starter. {this is a must-have for grilling}
When the coals are hot, place this around the outside of the grate, we are cooking the chicken with mostly indirect heat.
Close the lid to allow the temperature to get to 4500-475 degrees.
Add water, sea salt, sugar, and fresh lemon juice to a large bowl.
Submerge the whole chicken into the brine and brine for 2-4 hours or overnight.
After brining, rinse the whole chicken with cold water and pat dry using a paper towel.
Stuff the chicken with 1/2 stick of butter, half a lemon, and 8-19 cloves of smashed garlic.
Truss your chicken to ensure it cooks evenly
Brush or rub the chicken all over with a mixture of olive oil and melted butter.
Slice a large onion and place the slices in the bottom of a large cast-iron skillet.
Place the chicken on top of the onions, then place the skillet in the center of the grate.
Close the lid and cook the chicken for an hour.
Open the lid and baste the chicken with a brush with more of the olive oil and melted butter mixture as needed.
Close the lid and continue to cook for an additional 30 minutes, but check for doneness every 10-15 minutes.
Check the temperature using an instant-read thermometer. We're looking for a temp of 165 on the thickest part of the chicken thigh but not touching the bone.
When the chicken is done, use the oven mitts to safely remove the hot skillet,  then transfer the chicken to a clean cutting board and allow the chicken to rest for 15 minutes.
Carve the chicken and serve.