Grilled Three-Potato Salad

Name: Grilled Three-Potato Salad
Yield: 6 Servings
Ingredients: 1 pound red-skinned sweet potatoes (yams), unpeeled, scrubbed; 1 pound small Yukon Gold potatoes, unpeeled, scrubbed; 1 pound small purple potatoes, unpeeled, scrubbed; 1/2 cup mayonnaise; 1/4 cup fresh lemon juice; 2 tablespoons Dijon mustard; 2 teaspoons celery seeds; 1/2 cup plus 1 tablespoon chopped green onions