Boil chicken breasts in water that has been seasoned with salt and a little garlic powder. Boil until tender, then cool and shred the chicken. Save the broth and boil the noodles in it according to time on package. Drain, but save 2 cups of broth. Set aside.
Mix softened cream cheese, sour cream, and sauteed onions with the noodles. Add a little broth to thin mixture. Add a little black pepper, then set aside.
Mix shredded chicken, Rotel, and both soups. Mix well and set aside.
Spray a 9X13 baking dish with non-stick spray. Pour in half of the noodle mixture, top with half of the cheddar cheese. Add about half of the chicken mixture. Top with the remainder of the noodle mixture, then the remainder of the chicken mixture. Top this with the remainder of the cheddar cheese. Add a little of the reserved chicken broth for moisture. (The noodle mixture will continue to dry out as you are putting the casserole together.)
Bake uncovered in a 350 degree oven for 25-30 minutes until the casserole is hot and bubbly. Be careful that cheese does not overbrown.