Pre-heat oven to 200°C. Drizzle lamb with half the oil and coat with the Sichuan peppercorns. Season with sea salt. In a large non-stick frying pan sear the lamb for 5 minutes over medium high heat until evenly browned. Place lamb in a roasting dish and roast for 15 to 20 mins or until cooked to your liking. Set aside to rest for 10 minutes before thinly slicing lamb.
Meanwhile, heat the remaining oil in a wok over high heat. Stir fry garlic for 30 seconds. Add the asparagus, snow peas and mushrooms, and stir fry for 1 to 2 minutes, or until tender. Add bok choy and stir fry for a further 30 seconds, or until wilted.
Serve lamb with stir fried vegetables topped with green onions and chilli, if desired, and brown rice.