Melt butter in a 2-qt saucepan over medium heat. Stir in flour and cook for 1 minute. Add milk and bouillon and stir vigorously with a wire whip until mixture barely comes to a boil. Reduce heat and simmer for 5 minutes, whipping frequently. Keep warm.
Drain broccoli and divide in half. Chop 1/2 of florets into 1/4" pieces. Reserve. Heat a large saute pan over medium heat and add olive oil. Add all the broccoli, garlic, green onions and mushrooms to the saute pan. Cook, stirring constantly, for 2 minutes or until mushrooms begin to turn golden. Add the sauteed veggies and parsley to the warm sauce and stir well. Serve over hot pasta with Parmesan.
Source: The Olive Garden Style.