On a chopping board, dice the chicken thighs into 1-inch pieces and season liberally with salt and black pepper.
Warm the olive oil in a large saucepan over medium-high heat, then add the chicken and cook for 4-5 minutes, or until browned on all sides, working in batches if necessary. Remove the chicken from the saucepan, place it on a platter, and put it aside.
Reduce the heat to medium in the same pot, add the onion, carrots, and celery, and simmer for 3-4 minutes, or until the veggies are soft.
Cook for another minute, or until the garlic, ginger, turmeric, cumin, coriander, salt, and black pepper are aromatic.
Return the chicken to the saucepan, sprinkle with flour, and stir until thoroughly coated before adding the sweet potatoes.
Pour in the chicken broth and stir until everything is completely blended, scraping up any yummy pieces from the bottom of the saucepan.
Cook for 25-30 minutes, turning periodically, until the chicken is cooked and the sweet potatoes can be easily penetrated with a fork.
Cook for a further 5 minutes, or until the spinach has wilted, after adding the coconut milk and chopped spinach. Season with extra salt and pepper to taste.
The stew may be eaten immediately, and leftovers can be refrigerated for up to 5 days or frozen for up to 3 months in an airtight container.