Wash lettuce and baby vegetables, remove excess water. Slice onion thinly and soak in cold water to remove spiciness, then drain.

Mix soy sauce, sugar, mustard, salt, perilla oil, and vinegar to make the dressing. Use a sieve to blend mustard smoothly into the soy sauce.

Cut soft tofu into appropriate sizes. To easily remove tofu from packaging, cut two diagonal corners slightly and tap the packaging to release air.

Layer lettuce and soft tofu on a plate.

Pour soy sauce dressing over the salad right before serving.