Cook pasta in large saucepan of boiling salted water according to package directions until al dente. Drain, reserving 1 cup pasta cooking water. Place pasta in large bowl, add cauliflower.
Melt butter in same saucepan over medium heat; whisk in flour until smooth paste forms. Whisk in milk, salt and black pepper; cook 2 to 3 minutes or until thickened. Whisk in ½ cup reserved pasta water and Parmesan until smooth. Pour over pasta and cauliflower; stir to coat. Add additional pasta water by tablespoonfuls to loosen sauce, if needed. Stir in lemon peel, lemon juice and almonds. Top with arugula or gently fold into pasta mixture. Sprinkle with Aleppo pepper, if desired.
