Heat the oil in a saucepan, and add the sliced leek. Cook for a couple of minutes over a medium heat until starting to soften, then add the garlic and ginger. Cook for 2 more minutes, until soft and fragrant.
Add the vegetable stock, soy sauce, rice vinegar, sriracha, and plenty of black pepper. Mix well to create the broth.
Bring to a simmer, and add the Tenderstem broccoli. After a couple of minutes, add the rice noodles, and cook for a few more minutes until the noodles are cooked and the broccoli is tender but still fairly crisp.
Serve the noodle soup topped with sliced spring onions, red chillies, fresh coriander (cilantro), and a squeeze of lime juice.