In a mortar and pestle, combine 2 tablespoons olive oil, garlic, sage, fennel seeds, thyme, rosemary, 1 tablespoon black pepper, chile flakes and 2 teaspoons salt. Grind and pound the mixture into a smooth paste. Place the turkey breast skin side down on a clean flat surface. With a sharp knife, butterfly the turkey by cutting down the long side of the breast so it can open up like a book to create a large, flat rectangle of even thickness. Score the flesh lightly in a cross-hatch pattern, being careful not to cut too deeply into the flesh. Season the turkey with salt and black pepper. Rub the herb-spice paste into all the cuts on the surface of the turkey breast. Roll the butterflied breast together tightly starting with the side that does not have skin underneath it (that way there is skin on the outer layers when rolling it up). Form the turkey into a cylinder and secure with butcher¿s twine. Tie the roll every 1 1/2 inches, then place in the refrigerator for 4 hours uncovered; this will help the turkey firm up and allows the salt to do a short dry cure on the meat.
Preheat the oven to 350 degrees F.
Remove the turchetta from the refrigerator and bring to room temperature, about 30 minutes. Brush the turchetta with olive oil and season with salt and black pepper. In a cast-iron skillet over medium-high heat, brown the turchetta, 2 to 3 minutes per side. Arrange the turchetta skin side up and place the whole pan into the oven and cook until the internal temperature reaches 150 degrees F (carryover cooking will increase the temperature as the turchetta rests), about 1 hour 30 minutes. Remove from the oven, place on a large plate, tent with foil and rest 15 to 20 minutes. Add the chicken stock to the reserved juices in the pan and stir to combine. Keep warm.
To serve the turchetta, remove the string and use a sharp carving knife to slice it into 1-inch-thick medallions. Shingle the slices on a large serving platter, spoon cooking juice over the turchetta, and serve immediately.