In a food processor fitted with a metal blade, combine juice, sugar, salt, dry mustard and onion. After the ingredients are well blended, slowly add in oil.
Pour dressing ingredients into a jar. Add poppy seeds and shake well. Store in the refrigerator until needed.
Combine lettuce, pomegranate seeds, mango and apples in a salad bowl. Just before serving, drizzle some of the dressing on the salad and toss.
6 servings