Cut each salmon fillet into three bite-size pieces. Place cup mirin and cup soy sauce in a large shallow bowl with the salmon and set aside in the fridge to marinate for five-10 minutes. Slice mushrooms thinly, then place in a small saucepan with remaining mirin and soy sauce. Add sugar to taste and cook over medium-low heat for five minutes until mushrooms are softened and sauce is slightly reduced. Set aside.

Heat oven grill to high. Place salmon pieces on a foil-lined oven tray and place under grill for a few minutes until the top of the salmon becomes opaque. Turn pieces to cook the other side. Remove from grill and serve with mushrooms, brown rice and vegetables, with a squeeze of lime juice.