Heat cauliflower in pouches on full power for 9 to 10 minutes or until thawed.
In a deep, 2-quart, heat-resistant, non-metallic casserole place zucchini, onion and butter and heat, uncovered, on full power 3 minutes or until zucchini and onion are tender.
Add cauliflower in cheese sauce and tomatoes to onion-zucchini mixture.
Add salt and thyme leaves to mixture.
Heat, covered, on full power 5 minutes or until tomatoes are tender.