Step 1Heat oil in skillet over medium heat. Add onion and saute until tender, 5 minutes. Place onion and potato in food processor and puree until smooth. Combine tomato sauce and half-and-half in large saucepan. Bring to a boil and simmer 10 to 15 minutes. Add potato-onion mixture and cook, stirring occasionally, until thick and smooth. Add cheese. Mix chicken base with water and stir into soup. Simmer over low heat 5 to 10 minutes. Add dash oregano before serving.