Meanwhile, in 2-quart saucepan, heat squash and broth to boiling over high heat; reduce heat. Cover; simmer 15 minutes or until squash is tender. Stir in milk and taco seasoning. Return to boiling; remove from heat. Place squash mixture in blender. Cover; blend on medium speed 20 seconds or until smooth. Return to saucepan. Stir in 1 cup of the cheese until melted. Pour over pasta; mix well. Pour mixture into casserole. Top with tomato slices.