In the base of a slow cooker combine chicken stock, honey, chipotle paste, tomato puree and lime juice with smoked paprika, cumin, oregano, onion powder, garlic powder, salt & black pepper. Add chicken thighs and use your tongs to coat them.
Add the lid on and cook for 3-4 hours in HIGH or 6-7 hours on LOW. The chicken is cooked when it's piping hot through the centre and very easily falls apart.
Meanwhile, in a small bowl combine finely diced onion with lime juice and good pinch of salt & sugar. Leave to pickle for as long as the chicken takes to cook, tossing every now and then if you can.
Once the chicken has cooked, remove it from the slow cooker and place in a dish or curved baking tray. Pour the liquid into a pot or pan over medium heat and bring to a simmer. Combine 1 tbsp cornstarch/cornflour with 1 tbsp water then whisk into the sauce. Simmer until thickened (10mins or so).
Gently shred the chicken (don't over-shred in the first instance) then pour over your preferred amount of sauce. Toss to combine, shredding a little more if needed.
Serve in tortillas with cotija/feta, avocado, pickled onions and coriander/cilantro.(optional).