How to Make It
Place shiitakes and peppercorns in an 8-quart stockpot over medium, and cook, stirring often, until fragrant and peppercorns start to pop, about 8 minutes. Add soy sauce, Shaoxing, soy paste, tea, ginger, salt, 4 cups water, 1/2 cup garlic cloves, and 2 teaspoons cumin seeds to pot; bring to a boil over high. Reduce heat to medium-low, and simmer, uncovered, until flavors are infused, about 30 minutes. Remove pot from heat, and add scallions. Add ice; let stand, stirring occasionally, until ice is melted. Submerge chickens in brine, weighing them down if needed. Cover and chill at least 2 hours or up to overnight.
Remove chickens from brine, scraping off any solids stuck to skin, and set chickens aside. Pour 2 cups brine through a fine wire-mesh strainer into a small saucepan; discard solids and remaining brine. Bring reserved brine to a boil over medium, and cook until reduced to about 1/2 cup, about 20 minutes.
Open vents of a kamado-style grill completely. Light 2 charcoal chimney starters filled with lump charcoal. When charcoal is covered with gray ash, pour on grill’s fire grate. Insert cooking grate; close grill lid, and bring internal temperature to 250°F to 275°F. Maintain temperature 10 to 15 minutes.
Tuck wings under chickens. Place chickens, wing ends up, on vertical roasters with drip pans removed. Place roasters in a 16- x 12-inch aluminum roasting pan with handles; fill pan with remaining 5 cups water and remaining 1/4 cup garlic cloves. Brush chickens with 1/4 cup reduced brine, allowing excess to drip into pan. Transfer pan to center of grill. Close grill lid, and smoke, basting with pan drippings and remaining 1/4 cup reduced brine every 30 minutes, until a thermometer inserted in thickest portion registers 150°F, 1 hour and 30 minutes to 2 hours.
Brush chickens with pan drippings, and sprinkle breasts with remaining 2 teaspoons cumin seeds, pressing to adhere. Close grill lid, and continue smoking until skin is golden brown and a thermometer inserted in thickest portion of thigh and breast registers 160°F, 30 to 45 more minutes. Remove chickens from grill; let rest on roasters until thermometer registers 165°F, about 15 minutes. Transfer chickens to a serving platter. Garnish with lemon halves, and serve with pan drippings.