In a large saucepan, bring 1 in. of water to a boil. Add the potatoes, carrots and beans. Return to a boil. Reduce heat; cover and simmer for 10 minutes. Drain; place in a greased 2-1/2-qt. baking dish.
In a skillet, saute onions and garlic in oil until tender. Add tomatoes, cauliflower, celery and seasonings. Bring to a boil. Reduce heat; cover and simmer for 5 minutes. Spoon half over the potato mixture. Top with zucchini, green pepper and remaining tomato mixture. Cover and bake at 350° for 40-45 minutes or until vegetables are tender. Serve with a slotted spoon.