Preheat oven to 350 degrees F (175 degrees C). Prepare a 13x9-inch baking dish with cooking spray.
Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally until cooked through but firm to the bite, about 12 minutes. Drain.
Melt 6 tablespoons butter in a skillet over medium-high heat. Cook and stir mushrooms, onion, and celery in melted butter until just tender, 5 to 6 minutes; transfer to a large bowl.
Stir diced tomatoes, cream of mushroom soup, chicken broth, chopped green chiles, sour cream, seasoned salt, cayenne pepper, salt, and black pepper into the mushroom mixture. Add chicken and Cheddar cheese; stir. Gently toss the pasta with the mixture to coat the pasta completely; transfer to the prepared baking dish.
Mix bread crumbs and melted butter in a small bowl; sprinkle evenly over the pasta mixture.
Bake in preheated oven until hot and bubbly, 30 to 40 minutes.
