Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add green beans, cover, and steam until tender, 5 to 7 minutes. Drain, allow to cool slightly, and slice on the diagonal. Transfer to a bowl.
Mash tofu with a fork as much as possible. Mix in tahini and miso paste. Season with soy sauce, sugar, and salt. Blend with an immersion blender until it is the consistency of yogurt.
Pour dressing over green beans and mix to combine.
