Combine rice, cheese, onion, flour, salt, and pepper in medium bowl.
Beat egg whites with cream of tartar in small bowl until stiff but not dry.
Fold beaten egg whites into rice mixture.
Coat large skillet with nonstick cooking spray and place over medium heat until hot.
Spoon 2 to 3 tablespoons batter into skillet for each patty; push batter into diamond shape using spatula.
Cook patties, turning once, until golden brown on both sides.
Garnish as desired.