In a kettle, bring 2 1/2 quarts water with 1 tablespoon salt to a boil. Add 1 pound green beans, trim and cook them for 8 minutes or until they are tender but still crisp. Drain the beans in a colander; refresh them under running cold water and drain them well. Chill the beans. Slice thin 1/4 pound mushrooms and chill them. In a ceramic or glass bowl, combine well 3 tablespoons vegetable oil, 1 1/2 tablespoons each of red wine vinegar, lemon juice, minced onion, 1 tablespoon minced fresh parsley leaves, 1/2 teaspoon sugar, 1/4 teaspoon salt, and pepper to taste; let the dressing stand, covered, for 1 hour. Cut the beans into 2 inch pieces and in a salad bowl, toss them with the mushrooms and the dressing. Serves 4 to 6.