Place thawed turkey breast-side down. Using kitchen shears, cut along both sides of backbone and remove. Flip turkey breast-side up and press firmly on breastbone to flatten. Tuck wing tips under. Pat completely dry.

Shake Tony Chachere's injection well. Fill injector and inject into breast, thighs, and drumsticks in multiple spots until evenly distributed. Place on wire rack over baking sheet. Refrigerate uncovered 2–4 hours or overnight.

In small bowl, combine Tony Chachere's seasoning, garlic powder, onion powder, smoked paprika, and black pepper.

Brush entire turkey with melted butter and avocado oil mixture. Rub Cajun seasoning blend thoroughly over both sides of turkey.

Light full chimney of charcoal. Once ashed over, pour all coals on one side of grill. Place drip pan on cool side. Add 2-3 wood chunks on hot coals. Adjust vents to hold 275-300°F.

Place spatchcocked turkey skin-side up on cool side over drip pan. Insert probe thermometer into thickest part of breast. Smoke until breast reaches 165°F and thighs reach 175°F, about 2.5–3.5 hours. Add 10-15 coals every hour to maintain temp. Add fresh wood chunks every 45 minutes. Baste with melted butter every hour.

Optional: For crispier skin, move turkey over direct heat for final 5-10 minutes, rotating frequently.

Remove turkey and tent loosely with foil. Rest 30 minutes before carving.