Preheat oven to 350 degrees F.
Prepare spaghetti according to package instructions for al dente.
Melt butter in a large skillet over medium to medium-high heat, then add in bite size chicken pieces. Sprinkle onion powder over chicken, and add garlic to the pan. Saute chicken for about 7-10 minutes, until chicken is no longer pink.
To the skillet, pour in the canned soup, cubed Velveeta, cubed cream cheese, and diced Rotel tomatoes. Reduce the stove to a low heat, and cook the cheese mixture while stirring constantly until the cheese melts.
Once combined, add in drained pasta and stir it into the cheese and chicken mixture until it is fully coated. Season with salt and black pepper to taste.
Lightly grease a 2 quart casserole dish and pour in the cheesy chicken spaghetti from the skillet. Sprinkle the sharp cheddar cheese on top. Bake this in the oven for about 25-30 minutes, or until it’s heated thoroughly and the cheese on top is melted. Add the optional garnish of parsley or green onion on top, scoop it out of the dish to serve and enjoy!