Mexican chicken tortilla soup

Name: Mexican chicken tortilla soup
Prep time: 40 min
Cook time: 1 h 20 min
Total time: 2 h
Cuisine: Mexican
Ingredients: 1.2kg whole chicken; 5 fat red chillies 4 left whole but pierced a few times with a sharp knife, 1 sliced, to serve; 2 dried ancho chillies; 1 garlic bulb cut in half through the centre horizontally; bunch coriander stalks and leaves separated; 1 cinnamon stick; 3 tbsp vegetable oil; 2 large onions chopped; 1 tbsp ground cumin; 1 tbsp ground coriander; 1 tbsp smoked paprika; 2 x 400g cans tomatoes; 1 tsp sugar; 320g can sweetcorn drained; 400g can black beans drained; zest and juice 2 limes; 4 corn tortilla quartered and cut into strips; 2 avocados; 200g feta or queso fresco, crumbled, to serve