Prepare the Ingredients: Tear 150g ready-to-eat roast beef into bite-sized pieces. Cut ⅓ cucumber into thin strips. Roughly chop the coriander and the scallions.
Make the Oil Base: In a heatproof bowl, combine 2 tbsp minced garlic, 1 tbsp white sesame seeds, and cut dried chillies. Heat 1 tbsp oil in a small pan until it reaches roughly 180°C. Quickly pour the 1 tbsp hot oil over the mixture to let it sizzle and bloom.
Combine Seasonings: To the bowl with the hot oil mixture, add 1 tbsp light soy sauce, ½ tbsp dark soy sauce, 1 tbsp vinegar, 1 tbsp oyster sauce, and 1 tsp sesame oil. Mix well.
Mix Everything Together: Add the 150g roast beef pieces, cucumber strips, chopped coriander, and scallions into the bowl. Use tongs to toss until every piece is coated evenly in the dressing.
Taste, Adjust, and Enjoy: Give the salad a final taste. Add a splash more soy sauce or 1 pinch of salt if needed. Transfer to a plate and serve immediately, ideally with warm steamed rice.