Place the chillies in a small saucepan of water and boil for 5 minutes until softened. Remove from the heat and once cool enough to handle remove the seeds and stems. Roughly chop. Place them in the slow cooker with the chicken, chopped tomatoes, bbq sauce, garlic, sugar and spices. Cook on low for 6 hours.
Once the chicken is cooked remove it from the slow cooker and shred the meat. Reserve the bones to make stock if you're so inclined. Add a squeeze of lime juice to the lovely chipotle sauce that's in the slow cooker then blend up using a stick blender or pour it into a normal blender. Set aside while you assemble your quesadillas.
Heat a little oil in a frying pan over a medium high heat and crisp up some of the chicken (we used about half the chicken for our quesadillas and had lots of yummy leftovers), this will take about 5 minutes. Remove the chicken from the pan (but leave the pan on the heat) and assemble your quesadillas by topping one tortilla with some of the chicken, a drizzle of the chipotle sauce and a quarter of the cheese followed by another tortilla.
Add a tiny bit more oil to the pan. Place the quesadilla in the pan and cook for 2-3 minutes then flip and do the same on the other side. Set aside and repeat with the rest of the ingredients. Serve with salsa, sour cream and whatever else you fancy.