Gather all the ingredients. If you are going to make the mentsuyu from scratch, you can follow my recipe.
Put 2 tsp dried wakame seaweed in a small bowl and soak for 15 minutes. After soaking, queeze the water out and set aside.
Thinly slice 1 green onion/scallion.
Peel 1 Japanese or Persian cucumber (leave some skin for a striped pattern) and thinly slice diagonally. Then, cut into julienne strips and set aside.
Peel the skin from 2 inches daikon radish and grate the daikon. Squeeze the water out and set aside.
Bring a large pot of water to a boil for 2 servings udon noodles. My favorite udon is the frozen Sanuki udon. Blanch the frozen udon noodles in boiling water for 1 minute (no need to defrost). If you use dry noodles, follow the package instructions. Remove udon from boiling water and cool in an ice bath. Wait until it cools completely and drain.
To make the sauce, add ⅓ cup mentsuyu (concentrated noodle soup base). My mentsuyu recipe should be diluted about 2–3 times depending on your preference. If you use store-bought mentsuyu, read the directions to see if you can use it “straight” (no need to dilute) or if it should be diluted 2 or 3 times. Add ice cubes to keep the mentsuyu cool.
Serve the udon on the plate/bowl. Divide and add the toppings—the wakame, the cucumber strips, ½ cup tenkasu/agedama (tempura scraps), 1 soft or hard-boiled egg cut in half, and 4 cherry tomatoes. Sprinkle with ¼ tsp toasted white sesame seeds and the sliced green onions. Serve at the table with the mentsuyu and wasabi on the side. Pour the mentsuyu (sauce) on top and enjoy!