Position a rack in the middle of the oven and preheat the oven to 450 degrees.
Cut a deep, wide pocket in each pork chop. Sprinkle half the sage into each pocket and stuff each pocket with the cheese and prosciutto. Pat the chops dry and season with 1/4 teaspoon of salt and pepper.
Heat 1 tablespoon of the oil in a 12 inch, cast-iron skillet over medium high heat until it shimmers. Add the chops and cook until undersides are golden, about 2 minutes. Turn the chops, transfer the skillet to the hot oven to finish the cooking, 4 to 5 minutes, or until cooked through.
While the chops finish cooking, heat the remaining 1 tablespoon oil in a 5 quart pot over medium heat until it shimmers. Add the garlic and saute for about 30 seconds. Add the spinach and cook, covered, stirring occasionally, until wilted, about 30 minutes. Season with salt.
Transfer chops to plates. Add the butter and lemon juice to the hot skillet, stirring and scraping up the browned bits on the bottom, then pour the pan sauce over the pork. Serve with spinach.