1. In a large non-stick pan pour the vegetable oil and place it over medium-high heat. Once the oil is hot, add the green curry paste.
2. Stir well and gently stir fry the curry paste for about 2 minutes. Then pour in the coconut milk.
3. Stir well until the paste is more or less dissolved. Crush the lemongrass stalk under the blade of you knife and add it to the coconut milk together with the lime, the palm sugar (or caster sugar), fish sauce and the dried red chili pepper.
4. Simmer the curry sauce for 5 more minutes. Then add the cleaned mussels.
5. Shake the pan a little. Put a lid on the pan, turn the heat to medium and cook the mussels in the curry sauce for a good 6 to 8 minutes until the shells are all opened.
6. Check the seasoning and add extra fish sauce or sugar to taste if necessary. Take the pan off the heat. Divide the cooked mussels evenly over deep plates and drizzle with the remaining green curry sauce. Finish with some fresh cilantro. Serve immediately.