Preheat Oven: Preheat oven to 375°F (190°C).
Prepare the Pork Loin: Butterfly the pork loin by slicing it lengthwise, leaving about ½ inch uncut on one side, then open it like a book. Use a meat mallet or rolling pin to gently pound to an even thickness (~½ inch). Season both sides with salt, pepper, garlic powder, and Italian herbs.
Prepare the Stuffing: In a medium bowl, combine chopped spinach, ricotta, mozzarella, Parmesan, minced garlic, Italian seasoning, crushed red pepper (if using), and salt and pepper. Mix well.
Stuff the Pork Loin: Spread the spinach and cheese mixture evenly over the pork loin, leaving a small border along the edges.
Roll and Tie: Carefully roll the pork loin tightly from one end to the other. Use kitchen twine to secure the roll at 1–2 inch intervals.
Sear the Pork Loin: Heat olive oil in a large oven-safe skillet or roasting pan over medium-high heat. Sear the pork loin on all sides until golden brown, about 2–3 minutes per side.
Roast the Pork Loin: Transfer the skillet or roasting pan to the preheated oven. Roast for 50–65 minutes, or until the internal temperature reaches 145°F (63°C).
Rest the Pork Loin: Remove from oven and cover loosely with foil. Let rest for 10 minutes before slicing.
Slice and Serve: Remove twine and slice into 1-inch thick rounds to reveal the spiral of spinach and cheese. Garnish with fresh parsley and serve with lemon wedges if desired.