Boil 4 cups of water in a heavy-bottomed pan, add tea bags, and steep for 10 minutes.
Stir in sugar and salt. Stir until completely dissolved.
Add onion, lemon, garlic, and rosemary.
Add ice and cool completely.
Put the chicken into plastic bags, pour in the brine, place in fridge, and let marinate for 24 hours.
Take the chicken out of the brine and discard the brine. Dry the chicken off with paper towels.
Set up two-zone cooking. Heat one side of the grill to medium and leave the other side unlit. Put the chicken skin-side down on the side that is not lit. Cover the grill and cook for 20 minutes. Flip the chicken and cook for 40-50 minutes or until the thickest part of the chicken reaches 165°F.