Bake sweet potatoes at 375 degrees about 40 minutes, or just until tender when pierced with knife. Let cool, then peel and cut into generous l/2 inch dice. Bring l/4 inch layer of water to boil in large saucepan. Add snap beans and boil until water has cooked away and beans are tender. Add more water if necessary to prevent scorching. Let cool. Place peanut butter in large mixing bowl. Stir in garlic, ginger, soy sauce, sesame oil and wine vinegar until smooth paste is formed, then stir in l/2 cup water. Add sweet potatoes, beans, onion and hot chiles and set aside. Heat small, heavy skillet over medium heat. Add cumin seeds and toast, shaking pan, until seeds turn brown and fragrant, about 45 seconds. Be careful to avoid scorching. Remove from pan at once. Stir 2 teaspoons of seeds and l/2 teaspoon salt into salad and marinate l hour, stirring occasionally. Adjust seasonings to taste, adding remaining cumin, if desired.