Combine 1 quart water, 1/2 cup kosher salt and brown sugar together in a pot. Heat over medium heat just until the sugar and salt dissolve. Pour in remaining quart of cold water. Add in lemon, garlic cloves, 1 tablespoon granulated garlic and whole peppercorns. Allow to cool to room temperature.
Place chicken in a one gallon resealable plastic bag. Place bag inside a large bowl.
Pour brine over the top of chicken, seal and refrigerate for at least 2 hours but not more than 4.
Heat the grill to 425 degrees.
Discard the brine and carefully rinse and pat dry the chicken.
Combine avocado oil, remaining salt, granulated garlic and black pepper. Use a pastry brush and brush all over chicken.
Cook chicken skin side down, for 5 minutes. Reduce heat down to 350. Continue cooking chicken for 10 minutes or until it easily releases from the grill. Flip and continue cooking for another 10 - 15 minutes or until a meat thermometer inserted reads 165 degrees and the juices run clear. Serve.