Preheat oven to 350°F (175°C). Cook fettuccine according to package directions until al dente. Drain and set aside.

In a large skillet over medium heat, melt butter. Sauté onions and mushrooms until soft (about 5 minutes). Add garlic and cook for another minute.

Sprinkle flour over the mixture and stir well. Gradually pour in chicken broth and cream while stirring continuously until smooth.

Allow the sauce to simmer for about 3–5 minutes until slightly thickened. Stir in soy sauce and season with salt and pepper.

In a large bowl, combine cooked pasta, chicken, peas, and the sauce mixture. Mix gently until well-coated.

Transfer to a greased baking dish and top with mozzarella cheese. Bake for 20–25 minutes or until bubbly and golden brown.