Preheat oven at 180°C and potatoes into thin slices. Spread on a tray with non-stick baking paper. Drizzle with olive oil and rosemary. Bake until cooked and crispy. Briefly fry lemongrass stick and chopped chilli on olive oil. Put sea bass in the pan and fry until done. Take the fish out on the plate and fry spring onions for 3 minutes. Serve all together with a few splashes of soy sauce.