Cook noodles according to package directions; drain and set aside.
Meanwhile, toss panko with butter; set aside.
In a large saucepan combine green beans, mushrooms, red pepper, onion, celery, water, and garlic. Bring to boiling; reduce heat. Cover; simmer about 5 minutes or until vegetables are tender.
Stir soup and milk into vegetable mixture. Cook and stir until heated through. Remove from heat, then stir in cheese until melted. Stir in noodles and tuna.
Spoon mixture into a 2-quart casserole. Sprinkle panko mixture around outside edge of casserole. Bake, uncovered, in a 350 degrees F oven for 25 to 30 minutes or until tuna mixture is bubbly and panko is golden.