Preheat the oven to 180°C.
Cut all the Brussels sprouts in half and toss with olive oil and salt.
Pop these onto a baking tray cut side-down and bake for 30 mins, turning halfway through, until caramelised and crisp.
Grate the parmesan over the sprouts and then pop the tray back into the oven for 5 mins until the cheese melts.
Finely chop the parsley.
Pour the sprouts into a bowl and grate over more parmesan, lemon zest, orange zest and sprinkle over the parsley.