Preheat oven to 400°F. Coat 10-inch springform pan with nonstick vegetable-oil cooking spray.
Heat the oil in nonstick skillet over medium heat. Add the potatoes; cook, covered, stirring occasionally, for 12 minutes or until tender. Add 1/3 cup of the green onion, chili powder and 1/4 teaspoon salt if using; cook 2 minutes. Scrape into a bowl.
Coat skillet with nonstick cooking spray. Beat eggs, egg whites, corn, black pepper and the remaining 1/4 teaspoon salt, if using, in a bowl. Add to skillet; cook over medium heat for 2 to 3 minutes or just until set, stirring constantly. Scrape into a clean bowl. Wipe out skillet with paper toweling. Coat skillet with nonstick cooking spray.
Remove casings from sausage. Add sausage along with sweet red pepper and remaining green onion to skillet; cook 6 minutes or until sausage is no longer pink, breaking up sausage meat with spoon. Drain well. Stir in 1/4 cup of the salsa.
Place a tortilla in the bottom of prepared springform pan. Spoon on the potatoes, spreading evenly. Top with tortilla, pressing flat. Spoon on half of the sausage mixture, spreading evenly. Top with tortilla, egg mixture, tortilla, remaining sausage mixture and tortilla. Spoon on the remaining salsa. Sprinkle with the Cheddar cheese.
Bake in preheated 400°F oven for 40 minutes or until egg mixture is set, tenting loosely with aluminum foil during last 20 minutes. Let stand 10 minutes before serving. Remove sides of pan. Slice into eighths. Serve with reduced-fat sour cream, if you wish.