Preheat oven to 400 F.
Cook pasta al dente according to package directions.
Mince onion, and cube the chicken.
Bring a large oven safe skillet over medium-high heat and add 2 tsps. of oil.
Season the chicken with salt and pepper (½ tsp. each) and add into the skillet.
Cook the chicken until golden brown in color, then remove from skillet and set them in a bowl. Cover with aluminum foil wrap.
In the same skillet, melt the butter and sauté the onion until translucent in color.
Add in the sliced mushroom, garlic and continue sautéing for another 2-3 minutes until the mushroom is soft.
Add in the black pepper, salt, and flour. Mix together to blend very well.
Add in the half and half milk, chicken broth and mix well. Bring to simmer until the sauce thickens up.
Add in the cooked pasta, cooked chicken, green peas and mix everything together to coat with the sauce.
Top the dish with some mozzarella cheese. You can add as much as you want.
Baked in the oven for 30 minutes, or until bubbly and the cheese has obtained nice brown blisters.
Remove from the oven, top with some fresh chopped parsley and serve.