Preheat oven to Gas Mark 4, 180°C (350°F).
To prepare: Heat the oil and butter in a large ovenproof casserole dish over a medium-high heat. Season the chicken, then add it to the casserole and brown on both sides. The chicken doesn’t have to be cooked through at this stage. Transfer to a plate.
Add the bacon and onion to the casserole and cook until softened, about 3 minutes. Add the tomato purée, ginger and garlic paste, stir well and cook for about 1 minute. Add the stock and beans, bring to a simmer. Taste and season.
To cook: Add the chicken to the casserole and place, uncovered, in the preheated oven. Roast until the chicken is cooked through. This will take about 30 minutes. Remove from the oven, take out the chicken and stir the spinach leaves through the sauce.
To serve: Serve with rice or pasta and a green salad.