Preheat oven to 375 degrees. Spray a 9x13-inch baking dish with fat-free oil.
2
Cook broccoli and pasta to 3 minutes less than al dente in a large pot of salted boiling water per package directions. Drain and set aside.
3
Heat oil in a large nonstick skillet over medium-low heat. Cook onion, stirring, for 2 minutes or until soft. Add flour and cook, stirring, for 1 minute. Whisk in the milk and broth, increase heat to medium-high, and continue whisking until mixture comes to a boil. Cook about 7-8 minutes until the sauce is smooth and thick. Season with salt and pepper to taste. Remove from heat and stir in cheddar until melted. Add pasta and broccoli and stir well. Pour into prepared dish and top with breadcrumbs and Parmesan. Stir well.
4
Bake for 18-20 minutes. Increase oven to broil and cook until breadcrumbs are golden, keeping an eye on them so they do not burn, about 2 minutes.
