1 Carefully cut the tofu into 8 equal pieces and place on a shallow plate.
2 Squeeze lemon and measure 2 tablespoons juice. Mix juice with 2 tablespoons of mirin and soy sauce. Pour mixture over sliced tofu pieces and allow to marinate for 30 minutes, turning once at 15 minutes.
3 Bring 1 liter (approximately 4 cups) of salted water to a boil. Trim, rinse and cut scallions diagonally into thin rings. Peel and cut ginger root into thin slices.
4 Sprinkle the ginger and half of the scallions onto the tofu pieces. Place the plate of tofu in a steamer basket and place the basket over the boiling salted water. Cover and steam for 5 minutes.
5 Dissolve dashi in 3 tablespoons water. Whisk dashi together with remaining mirin and soy sauce. Drizzle steamed tofu with the sauce, garnish with remaining scallions, season to taste with pepper and serve.