Heat cauliflower in pouches in Microwave Oven for 9 to 10 minutes or until thawed. (Pierce holes in pouches with the tines of a fork to allow steam to escape.)
In a deep, 2-quart, heat-resistant. non-metallic casserole place zucchini, onion and butter and heat, uncovered, in Microwave Oven 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, in Microwave Oven 5 minutes or until tomatoes are tender.