Cook the pasta in salted water. In the last five minutes of cooking, add the green beans to the pot. Drain, and set aside with 1/2 to 1 cup of pasta cooking water.
Saute, stirring frequently, until the onion softens and turns translucent.
Heat the oil and add onion and garlic. Saute for five minutes until onions are translucent.
Add 1 pound of sliced button or cremini mushrooms and 1/3 cup of vodka
Saute the mushrooms until they start to caramelize and the liquid is mostly gone.
Add the sundried tomatoes and oregano
Add fresh-ground black pepper and salt to taste.
Stir everything together, then add the pasta and beans. Add 1/2 cup of the pasta-boiling water.
Toss together and continue cooking on very low heat another couple of minutes.
Stir in the walnuts.
Let the pasta stand another couple of minutes before serving.