Marinate the chicken in a large mixing bowl with chipotle paste and leave it in the fridge.
Peel the onion and slice the peppers in half lengthways, removing the seeds.
Place the onions and peppers on a baking tray and cook in the hot oven for 30 minutes until charred on the outside.
Heat a non-stick frying pan over medium heat and dry fry the spices for 1 minute until fragrant.
Peel the papery skin off the peppers carefully. Place them with the onion, fried spices, and tin of tomatoes in the blender and blend until smooth. Season with salt to taste.
Heat some oil in a casserole pot and fry the chicken until browned on both sides.
Add the sauce, and allow to cook down for 20 minutes.
Using 2 forks, shred the chicken. Allow to cook for a further 10 minutes. Serve with a squeeze of fresh lime juice and a dollop of sour cream.