Prepare the turkey breast by placing it skin-side down on a cutting board. With a sharp knife, butterfly the breast by cutting horizontally through the thickest part, opening it like a book but not cutting all the way through. Cover with plastic wrap and gently pound to an even thickness of about 1/2 inch using a meat mallet.
Preheat your oven to 375°F (190°C) and position the rack in the center of the oven.
Make the stuffing by melting the butter in a large skillet over medium heat. Add onions and celery, cooking until softened, about 5-7 minutes. Add the garlic and cook for another 30 seconds until fragrant.
Transfer the vegetable mixture to a large bowl and let cool slightly. Add breadcrumbs, cranberries, chestnuts, herbs, orange zest, chicken broth, and beaten egg. Season with salt and pepper and mix thoroughly until well combined.
Season the inside of the turkey with salt and pepper. Spread the stuffing mixture evenly over the butterflied turkey breast, leaving a 1-inch border around the edges.
Roll the turkey breast tightly, starting from the narrowest end, ensuring the stuffing stays inside. Tie with kitchen twine at 1-inch intervals to secure the roll.
Place the rolled turkey seam-side down in a roasting pan. Brush the entire surface with olive oil and season generously with salt and pepper.
Roast for approximately 60-70 minutes, or until an instant-read thermometer inserted into the thickest part reads 165°F (74°C). If the skin is browning too quickly, cover loosely with foil.
Allow the turkey to rest for at least 10-15 minutes before removing the twine and slicing. This crucial step ensures the juices redistribute for maximum moistness.
Slice into 1/2-inch rounds and arrange on a serving platter, showcasing the beautiful spiral of stuffing within each slice.