Heat oil in heavy large nonstick skillet over medium-high heat. Add onion and saute 5 minute Add green beans and cayenne pepper and saute until onion is translucent, about 3 minutes. Add zucchini, potatoes and parsley. Pour tomatoes and their juices over vegetables. Bring to boil. Reduce heat. Cover and simmer until potatoes are tender, stirring frequently, about 45 minutes. Season with salt and pepper. Remove from heat. (Can be prepared 1 day ahead. Cover and refrigerate.) Serve warm or at room temperature.