Preheat oven to 450°F (232°C).
Pat turkey dry with paper towels.
Place turkey breast-side down on a cutting board. Using kitchen shears, cut along each side of the backbone and remove it.
Flip turkey breast-side up, press firmly on the breastbone to flatten it until it cracks.
Melt butter in a saucepan with rosemary; keep rosemary in butter to infuse flavor.
Line a large rimmed pan with foil, spray with non-stick spray.
Spread chopped vegetables in the bottom of the pan, then place a rack over the veggies.
Season turkey generously with salt and pepper, place it on the rack, and brush all over with rosemary butter.
Add halved garlic heads around the turkey.
Roast turkey for 80-90 minutes, or until breast reaches 150°F and thighs 165°F internally.
Remove from oven, rest turkey for at least 20 minutes before carving.
Serve and enjoy!