Preheat the oven to 190°C (375°F).
In a saucepan, heat a little olive oil over medium heat. Sauté the shallots for 1 to 2 minutes. Add the port. Bring to a boil, then cook over medium heat until the liquid has been reduced by half. Add the demi-glace sauce and bring to a boil again. Reduce heat and simmer for 8 to 10 minutes, until reaching a syrupy consistency. Set aside.
Meanwhile, in a small bowl, mix the Chinese five-spice with the honey.
Pat the duck breasts dry with paper towels. Season both sides of the breasts with salt and pepper. Score the skin in a crisscross pattern, making cuts every 2 cm (¾ inch), taking care not to cut into the meat.
Place the breasts in an ovenproof skillet, skin side down. Sear for 8-10 minutes over medium heat, until golden brown. Remove excess fat from the pan during cooking.
Brush the breasts with the honey-spice mixture, then turn them skin side up. Transfer the skillet to the oven, and bake for 8 to 10 minutes. Transfer to a plate and let stand for 5 minutes, loosely covered with a sheet of aluminum foil, before slicing.
In a bowl, whisk Dijon mustard with apple cider vinegar, maple syrup and olive oil.
Add baby spinach, bean sprouts, Gala apples and red onion.
Add salt and pepper, and mix.
