Pennsylvania Dutch Corn Noodles

8 ounces medium-wide egg noodles, preferably yolk-free
2 tablespoons butter or margarine
1 large onion, quartered and thinly sliced
1 (16 ounce) bag frozen succotash (mixed corn
    and lima beans), thawed
1 1/2 pounds fresh, ripe tomatoes, diced, with 1/4 cup water
    (or substitute one 28-ounce can diced tomatoes)
1/4 cup chopped fresh parsley
Salt and freshly ground pepper

Begin cooking the noodles.

Meanwhile, heat the butter in a large skillet. Add the onion and saut