Season the chicken thighs with salt and pepper. If the thighs are large, you can cut them into smaller pieces for quicker cooking.
Heat a large skillet over medium-high heat. Add a bit of oil to the skillet and sear the chicken thighs until browned on both sides, about 3-4 minutes per side. Remove the chicken from the skillet and set aside
In the same skillet, add chopped onion and minced garlic. Saute until they become soft and fragrant, about 2-3 minutes.
Stir in tomato paste, ground cumin, dried oregano, and smoked paprika. Cook for another minute to toast the spices and enhance their flavors.
Return the seared chicken thighs back to the skillet. Pour in chicken broth until the chicken is almost covered. Bring the mixture to a simmer.
Reduce the heat to low and let the chicken simmer in the broth and spices for about 20-25 minutes, or until the chicken is cooked through and tender. You can cover the skillet partially with a lid.
Once the chicken is cooked, use two forks to shred it directly in the skillet. It should easily fall apart.
Warm the corn tortillas. Fill each tortilla with the shredded chicken birria mixture. Add any desired toppings such as chopped onion, cilantro, diced avocado, shredded cheese, and a squeeze of lime juice. Serve hot and enjoy your delicious Chicken Birria Tacos!