Low-Fat Cheesecake

9 whole low-fat cinnamon graham crackers, broken in half
2 tablespoons unsalted butter, melted
Cooking spray
2 8-ounce packages Neufchatel cream cheese, softened
2 8-ounce packages fat-free cream cheese, softened
1 1/2 cups sugar
1 cup reduced-fat sour cream
2 large eggs plus 3 egg whites
2 tablespoons all-purpose flour
1 teaspoon vanilla extract
1 teaspoon finely grated lemon zest
Assorted toppings