Mix the spice paste. In a large bowl, combine the garlic, garlic powder, onion powder, oregano, cumin, paprika, cayenne, salt, and pepper with 2 tbsp of the broth. Season the chicken. Add the thighs and turn until coated on all sides.
Sear. Heat the oil in a large skillet over medium high heat and sear the chicken for 3 minutes per side, until lightly browned.
Set aside. Transfer the chicken to a shallow dish and keep the bowl with the leftover seasoning.
Build the sauce. Reduce the heat to medium and add the rest of the broth, tomato paste, sugar, lime juice, and the leftover seasoning. Stir and bring to a simmer.
Shred and finish. Chop or shred the chicken, return it to the skillet, and simmer for 2 to 3 minutes, until the sauce is syrupy and the chicken reaches 165 degrees F. Add salt to taste.
Assemble. Fill warmed shells or tortillas with the chicken and finish with tomato, onion, avocado, cilantro, lettuce, cheese, and sour cream.