Stir the vinegar, water and sugar together until the sugar has dissolved. Add the red onions and radishes to the vinegar mixture, cover and refrigerate for at least 3 hours.
Combine the yoghurt with the chilli sauce, soy sauce and fish sauce. Cover and refrigerate the dressing until serving.
Cut the 2 baguettes into 4 pieces of equal size, then slit them open lengthwise – take care not to slice them all the way. Place the 8 pieces of bread on a parchment-lined baking sheet and heat them in the middle of the oven for approx. 5 min. at 200°C (conventional oven) – or use a toaster. Fill the warm bread with yoghurt dressing, lettuce, cucumber, salmon, pickled vegetables and coriander. Serve immediately.