Preheat the oven to 350 degrees F.
Prepare the spaghetti according to package instructions for al dente.
Melt butter in a large skillet over medium to medium-high heat. Add in the bite-sized chicken pieces and sauté until golden brown.
Sprinkle onion powder over chicken, and add minced garlic. Sauté until chicken is cooked through.
Pour in the cream of chicken soup, Velveeta, cream cheese, and diced Rotel. Stir until melted.
Add the drained spaghetti into the skillet, tossing to coat.
Season with salt and black pepper to taste.
Grease a 2-quart casserole dish and pour the mixture in.
Sprinkle the grated cheddar cheese on top.
Bake for 25 to 30 minutes, until heated through and cheese is melted.
Garnish with parsley or green onion and serve warm.