Heat a little olive oil in a saucepan and cook the onion and garlic with a pinch of salt over low heat for 4–5 minutes, until softened. Stir in the dried fruit (cutting larger fruit into small pieces), along with the sage and paprika. Let cook for 2 minutes, add the water, and let simmer for 5 minutes. Remove from the heat and let cool. Stir in the orange zest, chestnuts, hazelnuts, and spinach.
Open the pork, lay it flat, and season with salt and pepper. Top with the dried fruit mixture, leaving a 1¼ –1½-in. (3–4-cm) border all the way around. Starting at one long side, roll the meat up and tie it at regular intervals using kitchen twine. Preheat the oven to 350°F (180°C/Gas Mark 4).
Melt 3 tbsp (1¾ oz./50 g) butter in a Dutch oven over medium heat and brown the pork for 3–4 minutes on all sides. Place in the oven for about 5–10 minutes.
Wash the pears, cut them in half lengthwise, and coat with the lemon juice.
Melt the remaining butter, mix it with the maple syrup and chopped rosemary, and pour over the pears. Arrange the pears around the pork and cook, uncovered, for 50 minutes. Cover with the lid or aluminum foil and cook for an additional 10 minutes, or until the temperature of the meat reaches 145°F (63°C) in the center.
Remove from the oven and brush the roast pork with the warm jam. Cut into 1¼–1½-in. (3–4-cm) slices, garnish with rosemary sprigs and sage leaves, and serve with the pears.