In a large zipper-topped plastic bag or in a shallow dish, add the chicken, all of the spices, lime juice, and oil. Close the bag, and use your hands to mix everything together. If you are using a shallow dish, use tongs to work the spices evenly into the chicken. You can let this rest for up to a half hour or work with it right away. I like to let it marinate a minute to increase the flavor.

Heat a large skillet over medium to medium-high heat. When the skillet is hot, add the chicken. Cook for 12 to 14 minutes, turning once, until the chicken is cooked through. Remove the chicken from the pan, and let it rest for 10 minutes.

While the chicken cooks, heat the beans. If using black beans, mash them lightly with the back of a fork, and add a little water and salt to taste.

Preheat oven to 400 degrees F. While the chicken rests, prepare your tostada shells. Brush each side of a tortilla with oil, and place it on a baking sheet (about 6 fit on a sheet). Bake for 4 minutes. Remove from the oven, flip the tortillas over, return to the oven, and bake for 4 more minutes. Remove the shells for the oven, and allow to cool slightly. The shells will finish crisping up as they cool. Repeat with remaining shells.

Chop the chicken into bite-sized pieces, and prepare your other toppings.

To assemble your tostadas, add a tablespoon or two of mashed beans, a tablespoon or two of chopped chicken, and additional toppings to your liking. Eat right away.