About 2 hours ahead, mix the miso, orange juice, and orange zest together in a nonreactive bowl and set 2 Tbsp aside. Trim any excess fat from the duck breast and score the remaining fat with a sharp knife, then cut it into 2 even-size pieces. Put the duck breast into the bowl of orange miso and let it marinate for 2 hours.
Toward the end of that time, heat the oven to 400° F. Heat some olive oil in an ovenproof skillet over high heat. Drain any excess miso from the duck breast halves and place them, skin side down, in the skillet. Cook for 2 minutes, then turn over and place in the oven for 8 minutes longer to finish cooking.
Season the sugar-snap peas and mushrooms with sea salt and pepper. Place a skillet over medium heat and quickly sauté in olive oil for 2 minutes, then drain.
Toast the bamboo or banana leaves over an open flame and place in the empty orange shells. Place the duck breast halves inside the leaf-lined orange and drizzle the reserved orange miso over. Decorate with the mushrooms and peas, and place on a suitable serving dish.
Servings: 4