Preheat oven to 425°F (218°C).
Right before cooking, pat the duck dry with paper towels. Score the skin 1/2-inch (1 cm) apart to a diamond pattern (but careful not to score the meat).
You might need to cook the duck in two batches. Place the breast pieces in a cold ovenproof 12-inch heavy skillet, skin-side down. Cook over medium heat, until they’re gently sizzling. Turn to medium-low heat. Cook until the skin turns golden brown, for another 10 to 12 minutes. Flip them over every 3 to 4 minutes. If the duck skin cooks too fast, turn to low heat. Transfer the cooked duck onto a plate and cook the rest using the same method.
Arrange all the duck pieces in the pan, skin- side down. Transfer the skillet into the oven and bake for 8 minutes, until the skin turns dark brown. Flip to skin-side up and bake for another 6 to 8 minutes, until the skin turns dark brown but not burnt. Transfer the duck onto a big plate, skin-side up. Allow to rest for 10 minutes without cover before carving.
Prepare the sides while resting the duck.
If you plan to serve the duck later, wrap each duck breast with aluminum foil when they are warm enough to handle and seal in a bag. Store in the fridge for up to 3 days. When you’re ready to serve, warm them up in a preheated 300°F (150°C) oven for 10 minutes.
Serving option 1 - Easy weekday dinner
Transfer 1 tablespoon rendered duck fat into a large skillet. Cook the sweet potato first over medium heat until it’s tender. Then add the zucchini and sprinkle with salt. Cook until the zucchini just turns tender and the sweet potato is almost caramelized. Transfer the ‘noodles’ to serving plates.
Slice the duck into thin slices and place on top of the vegetables, with plum sauce on the side.
Enjoy hot as a main dish.
Serving option 2 - Fancy Peking duck rolls
To serve Peking duck style, steam the pancakes in a bamboo steamer for 3 to 5 minutes until hot.
Slice the duck and place them on a plate. Serve with hot pancakes, sweet bean sauce (or hoisin sauce), cucumber and green onions on the side.
To assemble - place one pancake in the palm of your hand, brush some sauce on the pancake, place 2 to 3 slices duck in the center, top with a few strips of green onions and cucumber. Roll and tuck the pancake like a mini burrito. Repeat, and enjoy hot as a main dish.