Heat the oven to 450°F/230°C. Score the fat on the belly and season both sides with salt and pepper. Make bed in a roasting pan with the vegetables. Lay the belly on top, skin-side up. Pour over the cider and a cup/250 ml of water. Cook 30 minutes to get the fat running. Stir together the honey and Dijon with a spoonful of water. Brush onto the fat and lower the heat to 325°F/160°C. Continue cooking, basting occasionally with the honey, for 3 hours.
Remove the belly from the oven when it’s done and transfer to a baking sheet. Return it to the oven at 450°F/230°C for 15 minutes to crispen the skin.
Meanwhile, drain the juices from the roasting pan into a measuring cup, reserving the vegetables and keeping them warm. Pour the fat off the juices, using some to moisten the lentils and saving the rest for another use. Deglaze the roasting pan with the vinegar and reduce to glaze, then add the cooking juices and cook down for a minute or two. Reheat the lentils gently.
Slice the belly and serve with the vegetables, and with the pork-fat moistened lentils.
An hour before the belly is done, start the lentils: Rinse them in cold water, drain, and put in a saucepan with 1-1/2 cups/375 ml water, the shallot and herbs.. Bring to a boil, cover, and simmer gently until tender, 30 to 40 minutes, checking occasionally to make sure no more water is needed. Drain, and season with salt and pepper. Set aside to reheat later.