Heat oven to 350°F. Spray 8-inch square (2-quart) glass baking dish with nonstick cooking spray. Cook rotini in large saucepan to desired doneness as directed on package, adding broccoli during last 5 minutes of cooking time. Drain; return to saucepan.
Meanwhile, spray medium saucepan with nonstick cooking spray. Heat over medium-high heat until hot. Add onion and garlic; cook and stir 2 to 3 minutes or until tender. Remove from heat.
Add milk and sauce mix; stir with wire whisk until well blended. Bring to a boil, stirring constantly. Reduce heat to low; simmer 1 minute, stirring constantly. Add American and Cheddar cheese blend; stir until melted.
Pour cheese sauce over cooked rotini and broccoli in saucepan; mix well. Spoon into sprayed baking dish. Sprinkle with Parmesan cheese. In small bowl, combine bread crumbs and margarine; mix well. Sprinkle over rotini mixture.
Bake at 350°F. for 25 to 30 minutes or until casserole is bubbly and topping is golden brown.