Wash the mussels under running water so that they are totally clean of beards. Discard all broken or already open shells. Put the in a saucepan with wine and bring to boil and cook until they have opened up. Take off the heat and let them cool down.
Use a sieve to separate the cooking mixture and the mussels. Throw away any unopened mussels. Collect the cooking liquid in a bowl and the mussels in another. Add the lemon juice to the cooking juice and season with salt and freshly ground pepper. This will make your dressing.
Cook the pasta according to packet instructions. This normally includes cooking them in salted water until they are tender but still firm to the touch. Drain them and cool under running water.
Add the prawns, mussels, garlic, parsley and spring onions to the pasta and stir to mix. You might have to cut the prawns in half if they are too large. Add the dressing and toss together everything. Refrigerate for a few hours so that the flavors blend together well. Check for seasoning before you serve. Its better if you let the pasta return to room temperature after the time in refrigerator before serving.