Place potato in a saucepan; cover with water. Bring to a boil; cook 8 minutes or until tender. Drain and cool. Toss potato with 1/4 teaspoon salt. Set aside.
Combine the Swiss chard and water in a large saucepan over medium heat. Cover and cook for 10 minutes or until Swiss chard is tender. Drain.
Combine 1/4 teaspoon salt, milk, and next 4 ingredients (milk through eggs) in a large bowl; stir with a whisk. Stir in potato and Swiss chard. Melt butter in a medium nonstick skillet coated with cooking spray over medium heat. Pour egg mixture into pan. Cover, reduce heat, and cook 10 minutes until almost set. Sprinkle with cheese.
Wrap handle of skillet with foil. Broil 5 minutes or until golden brown.