Dissolve 1 package Lime Jell-O in 1 cup hot water. Add 3 ⁄ 4 cup cold water, 2 tablespoons vinegar, and 1 teaspoon grated onion. Pour 1 ⁄ 2 cup mixture into 1-quart ring mold. Chill until firm. Chill remaining Jell-O until slightly thickened. Then fold in 1 cup cottage cheese, and 1 tablespoon mayonnaise; blend. Unmold. Garnish with salad greens. Fill center with seafood salad. Makes 6 servings.