Preheat oven to 350°F. Spray a 13x9-inch baking dish with cooking spray. Roughly chop the salad greens.
Cook pasta according to package directions. In the last minute of cooking, add the chopped greens. Cook until kale is wilted and pasta is al dente, drain. Transfer pasta and kale mixture to the prepared baking dish. Add the tomatoes.
Heat oil over medium heat. Add onion, garlic and mushrooms; cook 5 minutes or until onion is soft. Sprinkle flour over vegetables. Cook for 1 minute; stir in chicken broth. Cook and stir until thickened. Stir in dressing packet, crushed red pepper flakes and Gruyere cheese. Season with salt and pepper. Pour mixture over kale and pasta; stir to combine.
Crush croutons. Sprinkle croutons and Parmesan packet over top of pasta mixture. Bake 30 minutes or until bubbly and golden brown. Let stand 5 minutes before serving.