In a small bowl, combine the breadcrumbs and oil. Add 1 cup of cheese. Set aside.
In a saucepan over medium heat, melt the butter and cook the garlic for 1 minute, stirring with a wooden spoon. Incorporate the flour and continue cooking for another minute. Slowly add the milk and mustard and bring to a boil. Using a whisk, stir constantly for a few minutes, until the mixture thickens. Add the rest of the cheese. Season with salt and pepper.
In a large pot, cook the pasta in boiling water according to the directions on the package. Add the broccoli florets 1 minute before the end of the cooking time. Drain.
Combine the pasta and broccoli with the cheese sauce.
Pour the preparation into a buttered casserole dish. Sprinkle the breadcrumb mixture evenly over the top.
Bake for 10 to 15 minutes, until the top is golden.