In a large frying pan on medium heat, brown chicken breast in a little oil. Set aside.

Meanwhile, in a large pot on medium heat, saute onions til soft, about 10 minutes. Stir in garlic and cook another minute. Stir in seasonings.

In a large bowl, whisk masa with water til all lumps dissolve. Add to onion mixture and bring to a boil. Cook an additional 2-3 minutes, stirring constantly.

Add browned chicken, broth and tomatoes to onion mixture. Return to a boil, stirring occasionally. Reduce heat to medium low and simmer 15-20 minutes.

Remove from heat; add cheese and stir til it soup is smooth and cheese is melted.

Served with homemade tortilla chips and corn muffins.