Spanish Stewed Vegetables

1/4 c. olive or other cooking oil
1 medium-sized onion, sliced
3 medium-sized tomatoes, peeled and chopped, or 1 16-oz.
can (about 2 c.) tomatoes, cut up with a spoon
2 or 3 potatoes, peeled and quartered
1/4 c. finely chopped fresh parsley
1 clove garlic, minced, or 1/2 tsp. garlic salt

Heat oil in a large heavy skillet or deep pot. Add onion and cook until soft. Add zucchini, tomatoes, potatoes, parsley, and garlic. Cover and simmer over low heat until vegetables are tender (about 30 minutes). May be served hot or cold.