Soak 8 wooden skewers (or use metal ones). Slice the tuna and spring onions into 3cm chunks and mushrooms in half.
In a small bowl, mix the soy sauce, honey, ginger and lime juice. Thread the vegetables and fish onto the skewers. Brush each one with the sauce and then sprinkle over with the sesame seeds.
Cook under a hot grill for about 2 minutes each side, or alternatively on a griddle pan. Serve with steamed rice.