In a large, wide skillet, melt the butter over low heat. Add the onion and parsley and saute over medium heat until the onion turns translucent, about 10 minutes.
Add the sun-dried tomatoes and the chicken, if using, and saute, stirring often until the chicken colors, about 2 minutes. Add the wine and keep stirring over medium heat until most of it evaporates and the chicken is cooked through, about 4 to 5 minutes more.
Cook the gnocchi as directed above.
Add the chicken or tomato mixture to the hot bechamel sauce and mix well. Spoon generously over the gnocchi, and serve at once.