Drain and flake the tuna. Set aside. Cook noodles according to package directions. Drain and rinse in hot water. Combine noodles with the tuna, celery and green onions. Blend in the sour cream, mustard, mayonnaise, thyme and salt. Spoon half the mixture into a buttered 2 qt. casserole. Top with half the zucchini. Repeat layers. Top with cheese. Bake at 350 for 30 minutes or until hot and bubbly. Sprinkle with the chopped tomato. **Salmon may be used.