In a food processor, blend together all ingredients for the marinade until smooth paste has formed.
Place broccolini in oven-safe dish and pour over marinade, making sure each piece is thoroughly coated. Cover and leave to marinate in the fridge for at least an hour.
Meanwhile, preheat oven to 180˚C (360˚F).
Take broccolini dish out of the fridge, place into oven and cook for 20 minutes or until tender.
While broccolini is cooking, heat olive oil in a sauté pan over medium heat. Add onion and cook for 5 or so minutes, stirring regularly, until onion is turning translucent. Add brown sugar and cook for another 5 minutes until onion is caramelized.
Once broccolini is cooked, remove from oven, top with caramelized onions and crushed peanuts and serve immediately.