Cut the chicken breast into bite-sized pieces.

Melt 6 tablespoons of butter in a large skillet over medium heat.

Add the chicken, minced garlic, Italian or Greek seasoning, and cook until the chicken is fully cooked.

Remove the chicken from the skillet and set aside.

In the same skillet, add the chopped onions and mushrooms and cook until softened.

Add the remaining 2 tablespoons of butter.

Stir in the flour and cook for 2-3 minutes, creating a roux.

Gradually add the half and half and milk (or milk alternatives), stirring continuously to avoid lumps.

Continue stirring until the sauce is smooth and thickened.

Stir in the grated Parmesan cheese and the yellow and white cheese blend until melted and smooth.

Add the cooked chicken back into the sauce.

Add the chopped tomatoes, sour cream, and optional broccoli.

Cook fettuccine pasta according to package directions.

Drain the pasta and add it to the skillet with the Alfredo sauce.

Toss to combine, ensuring the pasta is coated in sauce.

Serve immediately.

Optional: For make-ahead preparation, pour the mixture into a large baking pan, cover, and refrigerate.

To reheat, preheat oven to 450°F (232°C) and bake covered for 45 minutes to an hour, or until heated through.