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.
This is a GREAT recipe, and to answer the previous reviewer, the "white sauce" recipe is linked from the list of ingredients, though I'm sure any white sauce would do. It's very easy to put together if you use a plastic bag to "pipe" the stuffing into the uncooked shells.