Pre-heat oven to 425 degrees C.
Place broccoli florets in a large bowl with a lid (or just use cling wrap) and drizzle in the olive oil, followed by the garlic salt and pepper.
Cover and toss.
Transfer the broccoli to a baking sheet and spread the florets out.
Grate parmesan over the florets.
Place in the oven and bake for 15 minutes, tossing the broccoli with a spatula once halfway through.