Preheat a waffle iron on medium heat and spray with cooking spray.
Mix mashed potatoes, eggs, flour, and salt in a large bowl. Stir in cheese and half of chopped green onions until just combined.
Scoop 1/2 cup of mixture into each section of Belgian waffle iron (1/3 cup for regular waffle iron) and spread evenly. Cook on medium until nicely browned and cooked through, about 5 minutes. Repeat with remaining potato mixture.
Serve waffles topped with sour cream, remaining green onions, and bacon.
Note: Nutritional analysis is per Belgian waffle.