MAKE the marinade by mixing together the mirin and 2 teaspoons of sugar in a small bowl until the sugar dissolves. ADD the miso, 1 tablespoon of soy sauce and the ginger and stir until well combined. SPREAD the mixture evenly over the salmon steaks and marinate, covered, in the refrigerator for at least 30 minutes. PREHEAT the oven to 400°F/200°C. LINE a baking tray with baking paper. PLACE the salmon fillets on the tray and bake for 20 minutes. WHILE the fish cooks prepare the spinach. MIX together 2 tablespoons of soy sauce, lemon juice, sesame oil and 1 teaspoon of sugar in a small bowl. HEAT a large pan over medium heat. TOAST the sesame seeds stirring constantly, until golden brown, then remove from the pan and set aside. HEAT the peanut or canola oil in the same pan. ADD the spinach and cook for 2 minutes, stirring regularly. POUR over the dressing, toss to combine, and cook for 1 minute. SPRINKLE over the toasted sesame seeds, and serve on plates with the salmon and cooked rice.