Place spinach between paper towels, and squeeze until barely moist; set aside.
Place a large nonstick skillet coated with cooking spray over medium heat until hot. Add onion and garlic; sauté 2 minutes. Add spinach; sauté 1 minute. Place mixture in a large bowl; set aside.
Combine ground chuck and turkey in skillet; cook over medium heat until browned, stirring to crumble. Drain and pat dry with paper towels; add to spinach mixture. Add egg substitute, 2 tablespoons Parmesan cheese, 1 teaspoon Italian seasoning, 1/2 teaspoon salt, and pepper; stir well, and set aside.
Combine tomato sauce, 1/4 teaspoon Italian seasoning, and 1/8 teaspoon salt in a bowl; spread 1 cup over bottom of a 13 x 9-inch baking dish coated with cooking spray. Preheat oven to 375º. Stuff each shell with 1/3 cup spinach mixture; arrange on top of tomato sauce mixture in dish. Pour remaining tomato sauce mixture over shells; spoon White Sauce evenly over tomato sauce mixture. Sprinkle with 3 tablespoons Parmesan cheese. Cover and bake at 375º for 30 minutes or until thoroughly heated.