Slice bacon into matchsticks. Peel and finely dice onion. Dice celery. Peel and finely dice carrot and sweet potato. Finely dice red chilli, if using. Cut chicken thighs in half.
If using a slow cooker, place all ingredients into the slow cooker, mix well then cover with lid and cook on low for 8 hours.
Heat oil in a large pan or stove-to-oven dish set over medium-high heat. Add chopped bacon and onion, and cook stirring, for 5 minutes for the bacon to begin to caramelise and the onion to become translucent.
Add the sugar and spices, except garlic, then stir and move the mixture off to the side of the pan - add chicken thighs and cook for 2-3 minutes on each side.
Add diced vegetables, pour in the diced tomatoes and passata, stir well to combine and dislodge any bits off the bottom of the pan.
Bring to a gentle simmer, then cover, lower the heat to low and cook, gently simmering for an hour. Season with salt to taste.
Once the meat is cooked through and tender, turn off the heat and using two forks shred the meat. Peel and finely chop the garlic. Stir through the shredded meat and sauce.
Serve with a generous sprinkling of Manchego or Parmesan and some sourdough bread on the side.