Cook the beans in boiling salted water for about 7 minutes. Wash the coriander and, except for something to garnish, roughly chop the upper 1/3 of the stems. Drain beans and rinse under cold water.
Wash and clean the tomatoes and cut into thick slices. Clean and wash spring onions and cut them diagonally into thin rings. Cut roast beef into wide strips. Mix oil, chili sauce and vinegar and mix with the remaining ingredients.
Season salad with salt, pepper and chili flakes. Garnish with coriander.