Mexican Tinga

Heat olive oil in a saucepan over medium heat. Add the onions; cook and stir until softened and translucent about 5 minutes. Meanwhile puree the tomatoes with chipotle peppers and adobo sauce to taste. Pour into the onions and add chicken. Cover and simmer for 20 minutes.

To serve mound the chicken onto tostada shells and garnish with a dollop of sour cream.