Preheat the oven to 190 °C (375 °F).
In a large pot of salted boiling water, cook the pasta al dente. Drain.
Use a knife to trim any excess fat from around the edges of the breasts. Make incisions in the duck meat in a checkerboard pattern, taking care not to cut into the flesh. Season with salt and pepper.
Preheat a large ovenproof skillet over medium-high heat. Place the duck breasts in the pan, skin side up. Cook for 2 to 3 minutes. Turn the breasts over and continue cooking for 2 minutes.
Turn the duck breasts over again and brush with half of the teriyaki sauce. Transfer the skillet to the oven and bake for 7 to 8 minutes.
Remove duck breasts from the oven and transfer to a cutting board. Cover loosely with a sheet of aluminum foil. Let stand for 5 minutes before slicing.
Meanwhile, in the same pan, heat the oil over medium heat. Sauté the onion, carrots, celery and pepper for 3 to 4 minutes.
Add the garlic to the pan and continue cooking for 1 minute.
Add the soy sauce, brown sugar, remaining teriyaki sauce and macaroni. Heat for 2 to 3 minutes over medium heat, stirring.
Slice the duck breasts.
Divide the macaroni between plates and top each serving with the sliced duck and green onions.
