To make sauce: With a fork, mix equal parts sesame oil and soy sauce in a small bowl until well incorporated.
To soft boil egg: Fill a small sauce pan with a few inches of water. Bring to a boil. Place egg in water and cook for 5-7 minutes. Egg pictured was cooked for 7 minutes, until just barely set. Peel egg and cut in half.
Cook soba noodles in boiling water over medium heat for 3-4 minutes (or according to package) and rinse immediately under cold water. Mix cucumber in with cold noodles. Toss with sauce. Place noodles and cucumber on plate. Sprinkle with scallion and cilantro. Place egg on top. Garnish with sesame seeds.