Preheat the oven to 350ºF. Cook pasta according to package instructions.
Meanwhile, prepare the sauce. Heat the oil in a small saucepan over medium-low heat. Whisk in flour, then slowly start to pour in milk, whisking constantly until smooth and no lumps remain. Whisk in nutritional yeast and 1 cup cheese, until cheese has melted. Once the sauce is smooth, remove from heat and whisk in salt, mustard, garlic powder, and pepper.
When the pasta has 5 minutes cooking time left, add broccoli florets to the pot and allow to cook until just tender. Drain the pasta and broccoli, and pour into an oven-safe baking dish. Pour cheese sauce on top and fold everything together.
Sprinkle remaining ½ cup cheese and the breadcrumbs onto the noodles. Bake pasta on the center rack for 25 minutes, until bubbling. Remove, garnish with additional nutritional yeast, and serve.