Spray an 8-by-8-inch baking dish with butter-flavored cooking spray.
In a large bowl, combine meat, spinach, bread crumbs, 1 teaspoon Italian seasoning, and 1/4 cup tomato sauce. Mix well to combine.
Pat mixture into prepared baking dish. Bake for 30 to 35 minutes.
In a medium bowl, combine remaining 1-1/2 cups tomato sauce, remaining 1 teaspoon Italian seasoning, sugar substitute, and mozzarella cheese. Spoon sauce mixture evenly over meatloaf. Continue baking for 15 to 20 minutes.
Place baking dish on a wire rack and let set for 5 minutes. Cut into 6 servings.