Easy Marinara Sauce

2 cans (14.5 oz each) Italian stewed tomatoes
1 can (6 oz) tomato paste
4 tablespoons chopped fresh parsley
1-2 cloves garlic, minced
1 teaspoon dried oregano
1 teaspoon salt
1/4 teaspoon ground black pepper
4-5 tablespoons olive oil
1/3 cup chopped onion
1/2 cup water

Combine first seven ingredients in a food processor or blender until smooth. Saute onion in olive oil for 2-3 minutes, until tender. Add tomato mixture and water; simmer for approximately 30 minutes.