Broccoli Cauliflower Salad

1 medium head cauliflower, broken into florets (about 7 ½ cups)
1 medium bunch broccoli, cut into florets (about 4 cups)
2 cups seedless red grapes
6 green onions with tops, sliced
2 cups (8 ounces) shredded part-skim mozzarella cheese
2 cups mayonnaise
¼ cup grated Parmesan cheese
2 tablespoons sugar
2 tablespoons white vinegar
½ to 1 pound sliced bacon, cooked and crumbled
Leaf lettuce
Additional red grapes, optional

In a large bowl, combine the cauliflower, broccoli, grapes, onions and mozzarella cheese. Combine the mayonnaise, Parmesan cheese, sugar and vinegar; pour over vegetable mixture and toss to coat.

Cover and refrigerate for at least 2 hours. Just before serving, stir in bacon. Transfer to a lettuce-lined bowl. Garnish with grapes if desired.