Fill a large saucepan with salted water and bring to a boil. Add the curry powder, let it dissolve then add the pasta. When the pasta is cooked but still firm drain and cool with running water. Drain again thoroughly and place in a large salad bowl.
Fill a large pot with salted water and bring to a boil. Boil the prawns until they turn pink and curl slightly, 2-3 minutes. Drain, place under cold running water and drain again. Peel and devein the prawns and set aside.
To the pasta add the cooked prawns, smoked salmon and green peas. In a small bowl stir together the tarragon, lemon juice, and salt and pepper to taste until well mixed. Add the oil and stir vigorously until blended.