Put minced garlic, chopped scallions, sesame seeds, and chili flakes into a small bowl. Heat oil until hot. Pour it over the above ingredients. Mix well.
Add sesame paste to another bowl. Stir with a spoon while adding 2 tablespoons of water in several batches until it becomes a smooth, much thinner consistency. Be patient with this process as it’ll take some time to get the right texture (see note 3 if using substitutes). Add light soy sauce, black rice vinegar, and sugar. Mix until fully integrated.
Cook the noodles
Bring plenty of water to a full boil. Put in noodles. Once it comes back to a boil, turn down the heat a little to avoid boiling over.
Once cooked, transfer the noodles to a colander and rinse under running water to cool them down quickly.
Assemble the dish
Place the noodles in 2 serving bowls. Top them up with cucumber, fresh chili, and cilantro (if using). Pour the spicy dressing and the sesame sauce mixture over.
Give everything a thorough mix to coat each strand of noodle with the sauce. Sprinkle some toasted sesame seeds to garnish.
Notes
1. To substitute Chinese sesame paste, you can use either peanut butter or a mixture of tahini and toasted sesame oil.2. If using fresh noodles, 7oz/200g makes a regular serving. If using dried noodles, calculate 3.5oz/100g for a serving. 3. If using peanut butter or tahini + sesame oil, you may need less water to thin the sauce. Adjust as needed.