Bring a large pot of salted water to a boil, add pasta, and bring the water back to a boil and cook for 8 to 10 minutes until tender, but still firm to the bite. In a skillet heat oil, add onions and cook for 2 minutes. Stir in chicken, walnuts, parsley and paprika and cook until heated through and chicken is cooked. Now remove skillet from heat and stir in yogurt. Season to taste with salt and freshly ground pepper. Drain, pat dry and transfer pasta to a serving dish. Add sauce and toss to combine. Serve immediately.