Peel the onions and garlic, then finely chop them in a small food processor. Set aside. Chop the mushrooms in the food processor as well and set aside. Cook the pasta for 10 minutes in boiling water with the bouillon cube.

Cut the chicken breasts into small cubes. In a Dutch oven or large pot over medium-low heat (about 285°F/140°C), melt the butter. Add the garlic and onions and sauté for about 10 minutes, until golden. Add the chicken cubes, season with salt and pepper, and cook on medium-low heat (about 285°F/140°C) until the chicken is tender and juicy.

Serve the pasta on plates. Top with the creamy chicken and mushroom mixture. Sprinkle with Parmesan cheese and parsley.