Grease a 9×13 casserole dish with Crisco and set aside. Preheat oven to 350 degrees F.

Combine butter, Velveeta, Rotel, cream of mushroom soup, and milk in a large stockpot. Cook, stirring, over medium heat until cheese is melted and smooth.

Add chicken, spaghetti, and salt and pepper. Toss to fully combine.

Pour the mixture into your prepared casserole dish and level the top with your spoon. Top with shredded cheese and sprinkle with breadcrumbs.

Cover with foil and bake for 30 minutes or until cheese is hot and bubbly.

Remove foil and broil for 3-5 minutes until breadcrumbs are lightly browned. Keep a close eye on it at this point. The breadcrumbs will burn quickly once they start to brown.

Remove from oven and let sit for five minutes.

Top with red pepper flakes, to taste, when you serve it.