Heat your oven to 350°F (180°C). Coat the chicken pieces lightly in seasoned flour (salt and pepper), then tap off any extra.
Warm half the oil in a large frying pan and add the bacon or pancetta along with the chicken. Cook for 10–12 minutes, turning until golden brown on all sides. Use a slotted spoon to transfer everything to a Dutch oven, then drain the fat from the pan.
Add the remaining oil to the same pan and sauté the onion, green bell pepper, and half the garlic for 5 minutes until softened but not colored. Transfer to the Dutch oven using a slotted spoon. Toss in the mushrooms, cook for 2 minutes, then add them to the pot as well.
Pour the wine into the pan and let it bubble until reduced to roughly ¼ cup. Add this to the pot along with the tomatoes, tomato paste, and sage. Cover and bake for 45 minutes until the chicken is fork-tender.
Mix the remaining garlic with parsley, lemon zest, and capers. Stir this mixture into the pot and adjust seasoning. Serve hot over mashed potatoes, garnished with fresh sage leaves.