Place the chicken, peppercorns, salt, garlic, and onion in a saucepan. Add the chicken stock and bring to a boil over high heat. Then cover, reduce the heat to a simmer, and cook for 45 minutes until the chicken is tender.
Remove the chicken from the liquid and set aside to cool. Add the cooking liquid to a blender and puree until smooth. Reserve for later use. When the chicken is cool, shred with two forks.
To make the tinga
Heat a large 12-inch sauté pan or cast iron skillet over medium heat.
Cook the chorizo until fully cooked and a little crispy, about 10 minutes.
Add the onions and garlic and sauté until soft and translucent, about 5 minutes.
Add the remaining ingredients along with the shredded chicken and 1 cup of the reserved cooking liquid. Then turn the heat down to a simmer and reduce until most of the liquid has evaporated, about 15–20 minutes. (Remove the cinnamon stick before serving.)
To finish the tacos
Serve with crispy tostadas or soft corn tortillas and your favorite taco toppings. We recommend avocado slices, fresh cilantro leaves, crispy jicama matchsticks or shredded cabbage, and a squeeze of lime.