Tinga de pollo, or shredded chicken, is a classic taco filling beloved for its flavorful sauce and simple preparation—in fact, it's a great way to use up leftover chicken! (Note: You may want to use tortillas from Chef Cámara's Homemade Corn Tortillas recipe on Panna.)
Poach chicken: In a saucepan, add chicken and enough water to cover by 1 inch. Add 2 pinches salt, onion, garlic, and cilantro. Bring to a boil, then reduce to a simmer and cook until opaque and cooked through, 20–30 minutes. Meanwhile, make Tinga Sauce.
Tinga Sauce: In a Dutch oven, heat oil over medium-high heat until smoking, 2 minutes. Add the onions (you should hear a sizzle when they hit the pan). Stir until lightly caramelized, 20 minutes. Meanwhile, place tomatoes, peeled garlic cloves, chipotle peppers, and chicken stock in a blender. Purée on medium speed until smooth, 30 seconds; then add tomato mixture to the onions. Stir and simmer, 5 minutes.
Remove chicken from poaching liquid. When cool enough to handle, shred by hand and add to Tinga Sauce. Check for seasoning, and add salt to taste (Chef Cámara adds 2–3 teaspoons). Simmer, 5 more minutes.
Assembly: Divide Chicken Tinga evenly among the tortillas. Garnish each with an avocado slice and a sprinkle of sea salt before serving.