Season the tuna steaks all over with the crushed peppercorns. Heat a griddle pan over a medium-high heat and griddle the tuna steaks for 2 minutes on each side until golden on the outside but still pink in the middle. Remove from the pan and leave to rest.
Drizzle the sugar snap peas with the sesame oil and steam over a saucepan of gently simmering water for 2–3 minutes or until tender.
Place all the dressing ingredients in a screw-top jar and shake vigorously until well combined.
Divide the sugar snap peas between 4 serving plates, cut the tuna steaks in half diagonally and arrange on the peas. Drizzle with the dressing and sprinkle with the sesame seeds. Serve immediately with rice noodles.