Heat a large saucepan over medium heat. Coat pan with cooking spray. Add onion; cook for 5 minutes or until tender, stirring occasionally. Add rice; cook for 1 minute, stirring constantly. Add water and salt; bring to a boil. Cover, reduce heat to low, and cook for 15 minutes. Stir in peas and grated cheese; cook 2 minutes, stirring constantly. Cover, remove from heat, and let stand 15 minutes.
Combine egg whites and egg in a large bowl. Add rice mixture, stirring until blended.
Heat oil in a nonstick griddle or large nonstick skillet over medium heat. Spoon 1/2 cup rice mixture per pancake onto hot pan, spreading each to a 4-inch diameter. Cook 6 minutes on each side or until the bottoms are browned. Garnish with shaved cheese, if desired.