Wash and dry chicken breast and cut into slices. Peel and dice onions. Clean and quarter mushrooms. Wash leek and cut into strips.
In a large pot, heat oil over medium-high heat, add chicken breast, and fry for approx. 3 – 5 min. Add onions, mushrooms, and leek. Season with salt and pepper.
Add chicken broth, cream, penne, and water to the pot and leave to simmer for approx. 10 – 15 min., or until pasta is al dente.
In the meantime, wash tomatoes and dice. Wash, dry, and finely chop parsley. Grate Parmesan. When pasta is al dente, remove pot from heat and stir in Parmesan and parsley. Serve in bowls, sprinkle with diced tomato, and garnish with Parmesan and parsley. Enjoy!