Tuna zucchini casserole

3 c zucchini sliced into 1/2 inch thickness
3/4 c shredded carrots
1/2 c chopped onion
5 tbs butter or margarine
1 6 ounce can tuna drained and flaked
2 1/4 cups herbed stuffing croutons
1 10.75 oz can cream of mushroom soup undiluted
1/2 c sour cream

cut zucchini slices in half cook in boiling salt water for 3 mins drain saute carrots and onions in butter till tender gently fold together cooked vegetables and tuna croutons soup and sour cream spread into greased 2 quart casserole bake 350 degrees 45 mins