For the pork, preheat oven to 175°C and arrange meat, skin side up, in a roasting dish. Pour juice and water around; add cinnamon, juniper and rosemary to the liquid. Rub sea salt into exposed skin.
Roast pork for 1 hour 20 minutes or until meat feels tender and pulls away from bone, and skin is crisp and puffed. Rest for at least 10 minutes before slicing.
While pork is roasting, make the relish. Heat the oil in a medium saucepan and sauté the red onion, garlic, ginger and spices for 2-3 minutes over a gentle heat until soft and fragrant. Add rhubarb, vinegar, sugar and zest, then simmer for 10-15 minutes or until rhubarb has softened and broken down.
Serve sliced pork with crusty bread, soft cheese and a dollop of rhubarb relish.