Heat margarine in wok. Add onion saute until translucent. Add garlic continue until onion golden. Add tomatoes, chiles, ginger, salt and spices. Bring to a simmer, then stir in potatoes, cauliflower, and carrots. Cover and simmer over medium-low heat for 10 min., stirring occasionally, then stir in the cilantro. Simmer for another 20 min over low heat, until vegetables and tender but firm. While cooking, there should be enough liquid to form a sauce; if needed add additional water, but not so much that becomes soupy.Steam string beans separately until bright green and crisp tender. Stir into vegetable mixture. Remove from heat and stir in yogurt. Serve at once.