Wrap tortillas in foil, or place in a tortilla warmer or similar dish, and place in a 350-degree oven.
Combine red onion, red wine vinegar, 1 tablespoon of water, ½ teaspoon kosher salt, and ¼ teaspoon granulated sugar and set aside to begin to pickle.
For quicker pickling, place the bowl in the microwave for 10 to 15 seconds until the liquid gets hot, then leave it aside to cool.
Spread chicken thighs out on a tray and sprinkle each side with the seasoning mixture of salt, cumin, chili powder, paprika, and pepper.
Heat a large skillet over medium-high heat and add 2 to 3 tablespoons of olive oil.
Arrange chicken in one layer and cook until browned underneath, about 4 to 5 minutes. Flip and cook until browned on the second side.
Transfer chicken briefly to a plate.
In the empty skillet, add garlic and cook for a minute until golden.
Add broth and scrape any stuck bits off the pan, bringing it to a simmer.
Return the chicken and any juices to the pan, reduce heat to medium, and cook for 3 to 4 minutes until the broth has reduced.
Shred the chicken in the pan with two forks or cut it into bite-sized pieces.
Assemble tacos by piling each warm tortilla with shredded chicken, any juices left in the pan, and all toppings.
