Put the garlic oil in a shallow baking tin and add the chopped rosemary and finely grated lemon zest. Tumble in the sprouts and mix everything together to coat well.
Roast the sprouts in the oven for 20 minutes then check the sprouts are cooked, giving them a few more minutes if not quite done.
When cooked tip the sprouts into a serving bowl and sprinkle with the cheese. Toss to combine and season to taste. Add lemon juice if you like, then serve.