Remove the skin and butterfly the turkey. Carefully slide your fingers between the turkey skin and meat, gently separating the skin while keeping it in one large piece. Set the skin aside. Place the turkey breast on a cutting board and holding a sharp knife parallel to the cutting board, slice horizontally through the thickest portion of the breast (starting at the middle and slicing toward the edge), stopping about an inch from the opposite edge. Open the turkey like a book, then cover it with plastic wrap and gently pound it to an even ½-inch thickness.
Cook the shallot and garlic. Heat the olive oil in a large skillet over medium heat. Add the shallot and saute for 2 to 3 minutes, until softened. Add the garlic and cook for another 30 seconds, until fragrant.
Add the apple and spinach. Add the diced apple and cook for 2 to 3 minutes, until softened. Add the spinach and cook for another 1 to 2 minutes, until just wilted and all liquid has evaporated. Remove from the heat and let cool to room temperature.
Stir in the cheese and seasoning. Once the filling mixture has cooled, add the gorgonzola, salt, and pepper, and stir together.
Fill the turkey. Preheat the oven to 400°F (200°C). Season the inside of the butterflied turkey lightly with salt and pepper. Spread the filling evenly over the turkey, leaving about a 1-inch border around the edges.
Roll and tie. Starting at one long edge, tightly roll the turkey into a log. Lay the turkey skin over the top of the roulade, wrapping it around as much of the turkey as possible, and secure with kitchen twine at 2-inch intervals. Brush the outside of the turkey with one tablespoon of olive oil and season evenly with the remaining salt and pepper.
Roast. Place the stuffed turkey breast in a baking dish or on a rimmed baking sheet. Roast for 40 to 55 minutes, or until an instant-read thermometer reads 155°F (68°C). If you'd like the skin extra crispy, you can turn on the top broiler in the last minute or two of cooking.
Rest and slice. Transfer the turkey to a cutting board, tent it with foil, and let it rest for 10 to 15 minutes. While resting, it should increase in temperature to 165°F (74°C). Remove the kitchen twine, slice into ½-inch rounds, and serve.