Sauté broccoli, mushrooms and garlic in olive oil for roughly 5-8 minutes.
Preheat oven to 400 Degrees.
While the veggies are cooking boil water and cook pasta, but drain before it cooks all the way. Set aside.
In a large saucepan melt the margarine over medium heat. Add the flour and salt and stir to combine. Cook the butter and flour mixture for roughly 1 to 2 minutes. Gradually whisk in the chicken broth to the flour mixture.
Stirring constantly, gradually bring the mixture up to a boil, keep whisking-about another 2 minutes This thickens the sauce. Turn down the heat, and then simmer for an addition 2 minutes until the mixture thickens even more. Remove the pan from the heat and stir in the milk and Parmesan until the cheese melts.
Spray 2-two quart baking dishes or one large baking dish with cooking spray. Add sautéed veggies to the drained pasta. Pour most of the sauce into the mixture (leaving about 1/2 cup sauce).
Sprinkle the mozzarella cheese evenly over the top and pour the remaining sauce around the edges of the dish(es).
Cover and bake for 25 minutes. Uncover and cook for another 5 minutes.