Make the sesame dressing: add onion and pear into a food processor and puree until smooth. Alternatively, grate them using a fine grater or a microplane. Transfer puree into a small bowl. Add soy sauce, lemon juice, sesame seeds, sesame oil, and rice vinegar. Mix well to combine and store in the fridge while preparing the salad.
Fill a pot or saucepan with water and bring to a boil over medium-high heat. While waiting, prepare a mesh strainer or a slotted spoon, a mixing bowl, and a colander in the sink.
Once the water starts to boil, add the sprouts and let cook for 1-1½ minutes or until desired crunchiness. Fish them out using a strainer or slotted spoon (do not discard the boiling water), shake off the excess water, and transfer to a mixing bowl.
Repeat the same process with the carrots, but cook for only 30-60 seconds or until desired crunchiness. Fish them out, shake off excess water, and transfer to the same mixing bowl.
In the same boiling water, cook soba or buckwheat noodles for about 4 minutes or per package directions. Drain the noodles into the colander, run cold water over them to quickly cool the noodles, drain well, then transfer to the mixing bowl.
Into the same mixing bowl, add sliced cucumber, along with the sesame dressing. Toss to coat. Cover then place in the fridge to chill until ready to serve or for up to 2 days if making ahead.
To serve, divide your dressed salad into three bowls, top with lettuce and garnish with a sprinkle of sesame seeds (optional). Enjoy!