Preheat oven to 350 degrees.
Heat oil in large skillet.
Saute onions and green peppers 3 minutes, stirring now and then.
Add zucchini and mushrooms and saute another 3 minutes, stirring a few times.
Add tomato, salt, pepper and thyme. Saute 3 minutes more, stirring a few times.
Butter 2 quart casserole and spread stuffing in bottom.
Layer ½ vegetable mixture over stuffing.
Cover with 1 cup cheese
Layer remaining vegetables and the other cup of cheese.
Bake for 30 minutes.