TO BRINE THE CHICKEN: Combine garlic heads, bay leaves, and salt in gallon-size zipper-lock bag. Press out air and seal bag. Using rubber mallet or meat pounder, pound mixture until garlic cloves are crushed. Transfer mixture to large container or stockpot and stir in 2 quarts cold water until salt is dissolved. Immerse chicken in brine and refrigerate until fully seasoned, about 2 hours.

FOR THE GARLIC-PEPPER OIL: While chicken is brining, heat garlic, black pepper, pepper flakes, and oil in small saucepan over medium heat until garlic is fragrant and sizzling and mixture registers about 200 degrees on instant-read thermometer, about 3 minutes. Remove from heat and cool to room temperature, about 40 minutes. Measure 2 tablespoons garlic-pepper oil into 2 small bowls and set aside.

TO FLAVOR THE CHICKEN: Remove chicken from brine and thoroughly pat dry with paper towels. Apply 2 tablespoons infused oil beneath skin.

TO GRILL THE CHICKEN: Turn all burners on gas grill to high, close lid, and heat until grill is very hot, about 15 minutes. Scrape grill grate clean with wire brush; lightly dip small wad of paper towels in vegetable oil and, holding wad in tongs, wipe grill grate. Turn all burners to medium-low, position chicken skin-side down in center of grill grate, cover.

Cook until instant-read thermometer inserted into thickest part of thigh registers 170 to 175 degrees, 30 to 40 minutes. Transfer chicken to cutting board; let rest 10 minutes. Carve, then drizzle carved chicken with remaining infused oil and serve with lemon wedges.