Place a medium-sized pot over high heat and add the cooking oil. Once it’s hot, add onion, tomatoes, garlic, guajillo chiles, arbol chiles and bay leaves. Stir for a few minutes until everything starts to soften up.
Add the chicken and all of the spices to the pot. Stir everything together, then add enough chicken broth to cover up the chicken. Bring this mixture up to a boil, then reduce heat to low, cover with a lid, and simmer for 30-40 minutes or until the chicken is cooked through.
Once the chicken is cooked through, use a fork to shred the chicken directly in the pot. Once it’s shredded up, add another cup of chicken broth if needed and bring it back to a simmer for about 10 minutes. This will help infuse all of those flavors into your tacos.
Warm up your corn tortillas on a hot skillet or comal to assemble the tacos. Place two tablespoons of chicken birria onto each tortilla and top with cheese, onion and cilantro. Serve immediately.