In large pot, place oil, chicken base, onion and spices. Saute until onions are soft and clear, about 5 minutes.

In another container, combine masa harina with 1 quart water. Stir until all lumps dissolve. Add to sautéed onions; bring to boil.

Once mixture starts to bubble, continue cooking 2 to 3 minutes, stirring constantly. This will eliminate any raw taste from masa harina.

Add remaining 3 quarts water to pot. Add tomatoes; let mixture return to boil, stirring occasionally.

Add cheese to soup. Cook, stirring occasionally, until cheese melts. Add chicken; heat through.