Score the skin of the duck breast at 2cm intervals, then season with sea salt and black pepper. Place the duck skin-side down in a cold non-stick frying pan, then turn the heat on to medium-high. Cook for 8 minutes without moving it, or until the fat is well rendered and the skin is golden and crispy. Meanwhile, finely chop the bacon. Peel and finely slice the garlic. Turn the duck over and cook for 4 minutes on the other side, then remove to a plate to rest, leaving the pan of duck fat on the heat. Sprinkle the bacon and garlic into the hot pan, strip in the rosemary leaves and cook for 2 minutes, or until golden, stirring regularly. Add a splash of red wine vinegar and stir to pick up any sticky bits, then pour in the beans, juice and all. Simmer for a couple of minutes, then stir through the spinach until wilted. Slice the duck breast at an angle. Divide the beans between your plates and arrange the duck on top, spooning over any resting juices, to finish.