Slice zucchini in 1/2 diagonal slices.
Saute onion in butter until tender.
Add zucchini and seasonings - mix well and simmer about 15 minutes (until zucchini is tender).
Add tomatoes and corn and cook uncovered for 5 minutes on low heat.
Place in shallow casserole - top with mayonnaise and cheese which have been blended.
Broil 6 from element until lightly browned.