1. Preheat oven to 350 degrees F.
2. In a medium saucepan, melt butter over low heat. Stir in the flour, add milk and chicken broth, cooking until thickened.
3. Mix in noodles, sour cream, lemon juice, spinach, mushrooms, water chestnuts, pimiento, onion, celery and seasoned salt.
4. In a greased 4-quart baking dish, alternate layers of noodle mixture and chicken. Top with grated cheese and bake for 30 minutes.