Heat olive oil in a large skillet over medium heat. Add the onion and a pinch of salt; sauté until translucent and slightly caramelized, 5–7 minutes.
Add garlic and cook for 30 seconds until fragrant. Don’t burn it; garlic and heat are best frenemies when they cross paths too long.
Push onions to the side, lay the chicken thighs in the pan, and season with salt and pepper. Sear for 2–3 minutes per side until they start showing a golden edge.
Reduce heat to medium-low. Stir in chipotle tomato sauce, cumin, oregano, paprika, and chili powder. Mix well to coat the chicken.
Simmer gently for 15–20 minutes, or until the chicken is cooked through and shreddy. Shred the meat with two forks right in the sauce, letting it soak up all that smoky goodness.
Taste and adjust salt, pepper, or heat. If you want more char, raise the heat for a minute and let the edges get a little crispy.
Warm the tortillas in a dry skillet or microwave them until flexible. Spoon the tinga onto each tortilla and pile on toppings if you like. Serve hot.