Bring large pot of salted water to boil for pasta and broccoli. Cook pasta and broccoli together, according to package directions for al dente, and drain.
Make bread crumb topping:
In small bowl mix together bread crumbs and 1 tbs. olive oil. Set aside.
Preheat oven to 375 degrees F. Spray a baking dish with cooking spray.
While pasta cooks, heat a large sauce pot over medium heat. Add 2 tbs. olive oil, onion and garlic. Cook stirring occasionally for 1 minute. Add 4 tbs. butter and melt, then add flour. Whisk until roux bubbles, then cook for 1 more minute.
Whisk in milk, stock, ground mustard and cayenne pepper. Bring to a boil. Simmer sauce stirring occasionally for about 5 minutes.
Remove from heat add cheese and season with salt and pepper to taste. Mix well until cheese melts.
Add drained pasta and broccoli to cheese sauce, mix well to combine. Transfer to baking dish. Top with bread crumb topping and spray lightly with cooking spray.
Bake for 30 to 40 minutes, until brown and bubbly.