Dice 2 large chicken breasts into bite-sized pieces. Melt 6 tablespoons of butter in a large skillet over medium heat. Add chicken, season with 1 tablespoon of Italian seasoning, and cook until fully done. Remove chicken but leave the pan drippings.
Bring a pot of water to a boil and cook spaghetti noodles until al dente. Drain but do not rinse!
Reduce heat to low. Add 1 tablespoon minced garlic and 1 tablespoon minced onion to the pan. Sauté for about 1 minute, but don’t let them burn. Stir in ¼ cup flour and cook for 1 minute to remove the raw flour taste. Gradually add 1 ½ cups chicken broth, stirring until smooth. Pour in 1 1/2 cup heavy cream and let the sauce simmer on low for 5-6 minutes until it thickens.
Blend 8 ounces cream cheese with 1 ½ cups of the sauce in a blender for a super smooth, creamy texture. (Alternatively, melt the cream cheese slowly in the skillet, but this takes longer.) Return the blended cream cheese mixture to the pan.
Stir in 2 undrained cans of Rotel and 1 ½ cups freshly grated cheddar cheese. Let the cheese melt into the sauce.
In a 9×13 casserole dish, add the cooked spaghetti. Toss with 1 tablespoon of olive oil to prevent sticking. Add the cooked chicken and pour the cheese sauce over everything - season with salt and pepper. Mix well.
Place the casserole dish in the oven and bake at 400°F for 10 minutes to meld the flavors.
Garnish with fresh parmesan cheese and parsley. Enjoy!