3ouncesshredded sharp cheddar cheeseor Monterey Jack or Queso Fresco
sour creamor Mexican Crema
chopped fresh cilantro
Stir together tomatoes, onion, garlic, cumin, oregano, and chili powder in a large saucepan over medium heat; bring to boil. Add chicken thighs (or boneless skinless chicken breasts if you prefer) and season with salt and pepper. Stir to coat chicken with tomato mixture then spread into an even layer. Reduce heat and cover; keep at a low simmer for 35-45 minutes, until chicken is tender and easy to shred. Transfer chicken to cutting board. Increase heat and return sauce to boil; cook, stirring occasionally, until most of the liquid has evaporated (it should look like a very thick salsa), 8-12 minutes. Remove from heat.
While sauce reduces, shred chicken into bite size pieces using two forks. (If making bite-size tostadas chop shredded chicken into pieces small enough to fit on the chips without hanging over the side.)
Once sauce has reduced, return chicken to sauce and place over medium heat; cook and stir until heated through. (If it looks like more sauce than you want, transfer ⅓ to ½ of it to a separate bowl, stir the chicken into the remaining and add back sauce until you reach your desired consistency.)
To make the guacamole: In a large bowl, mash together avocado, pico de gallo and fresh lime juice. Season to taste with salt.
To assemble bite-size tostadas: on one chip, spread about a teaspoon of warm refried beans followed by a large pinch of chicken, pinch of cheese and a small dollop each of guacamole and sour cream. Sprinkle with fresh cilantro if desired. Repeat with remaining chips. (You can also do this assembly style, adding the layers in order to a whole tray of chips.) Serve.
To assemble full-size tostadas: spread on a thin layer of warm refried beans followed by a thin layer of chicken. Sprinkle with cheese and top with guacamole and sour cream. Sprinkle with fresh cilantro if desired. Repeat with remaining tostada shells.
Note that the nutrition information is for each bite-size chicken tostada. If you make 12 full-size tostadas (using the Tostada Shells) with the same proportion of toppings, they'll have ~250 calories each.
If you prefer to use bone-in skin-on chicken breasts see my Chicken Tinga post for detailed instructions. To use Shredded Chicken, or rotisserie chicken for this recipe, follow the instructions for the sauce, but reduce the covered cooking time to 20 minutes. Then reduce the sauce uncovered until thickened to the consistency of a thick salsa. Stir in shredded chicken; reduce heat and simmer 5-10 minutes to reheat the chicken and allow it to soak up plenty of flavor.