Prepare the flavour base. Heat a splash of oil in a large frying pan over a medium heat. Add the diced onion and cook for 5-6 minutes, stirring occasionally, until the pieces turn translucent and glossy, and you can smell their sweet, mellow aroma. Add the minced garlic and cook for another minute, just until it becomes fragrant—you will notice the scent shift from raw to gently toasted.

Bloom the spices. Stir in the cumin, smoked paprika, oregano, ground coriander, cayenne, salt, and pepper. Cook for 30 seconds, stirring constantly, until the spices release their oils and the mixture becomes darkly fragrant and slightly paste-like. This step is key—it wakes up the spices and gives the final dish a much deeper character.

Add the tomato elements. Pour in the chopped tomatoes and the tomato purée, stirring to combine everything into a thick, ruddy sauce. Let it simmer for 2 minutes, until it darkens slightly and you can see small bubbles breaking the surface. The sauce should look rich and smell intensely savoury.

Assemble in the slow cooker. Place the chicken thighs in the slow cooker in a single layer if possible. Pour the tomato-spice mixture over the top, then add the chicken stock, lime juice, and bay leaves. Gently nudge the chicken so it is mostly submerged. The liquid should come about halfway up the chicken—the meat will release its own juices as it cooks.

Cook low and slow. Cover the slow cooker with its lid and cook on low for 6-7 hours, or on high for 4 hours. You will know it is ready when the kitchen is filled with a warm, layered fragrance and the chicken is so tender that it falls apart at the prod of a fork. The sauce will have darkened and thickened slightly.

Shred the chicken. Using two forks, gently shred the chicken directly in the slow cooker. The meat should pull apart with almost no resistance, creating soft, juicy strands. Stir the shredded chicken back into the sauce, letting it absorb the liquid. If the mixture looks a little loose, leave the lid off for 10 minutes on the keep-warm setting to let it reduce slightly.

Finish and serve. Remove the bay leaves and taste the filling, adjusting the salt or lime juice as needed. The final texture should be moist and clinging, not soupy. Pile the warm, spiced chicken onto soft corn or flour tortillas and serve immediately.