Preheat the oven to 425 degrees.
Spray a 9" pie pan with cooking oil spray.
Heat olive oil in a medium skillet over medium heat. Add diced onion and cook until softened. Add chicken sausage and cook until browned and cooked through. Set the skillet aside to cool.
In large bowl, whisk eggs, milk, salt and pepper until blended and smooth. Add diced bell pepper, 1 cup of Gruyere and 1/4 cup of Italian parsley. Add sausage mixture. Pour the batter into the prepared pie plate. Sprinkle with the remaining cheese. Bake for 25 to 35 minutes or until golden brown. Garnish with chopped parsley. Serve hot.