Heat the olive oil in a large heavy-bottomed pot over medium heat. Add the diced onion and cook, stirring occasionally, for about 5 minutes until it softens and starts to turn translucent at the edges. Add the garlic and cook for another 60 seconds, stirring so it does not burn.

Stir in the tomato paste, smoked paprika, cumin, coriander, red pepper flakes, salt, and black pepper. Cook everything together for about 90 seconds, stirring constantly. The paste will darken slightly and the spices will smell fragrant. That is what you want.

Pour in both cans of fire-roasted tomatoes with all their liquid, then add the chicken broth. Stir to combine, scraping up anything that stuck to the bottom of the pot. Nestle the chicken thighs into the liquid so they are mostly submerged. Bring to a gentle boil, then reduce the heat to medium-low, cover, and simmer for 25 minutes.

After 25 minutes, pull the chicken thighs out onto a cutting board. They should be cooked through and very soft. Shred them using two forks, pulling the meat apart into rough pieces. Do not over-shred into dust, you want some texture. Return the shredded chicken to the pot and stir in the drained chickpeas.

Let the stew simmer uncovered for another 4 to 5 minutes so it thickens slightly and the chickpeas warm through. Taste the broth and adjust salt if needed. Add the lemon juice and stir.

Turn the heat to low and add the spinach in two or three batches, stirring after each addition. It wilts down in about 60 to 90 seconds total. Once the spinach is fully wilted and bright green, pull the pot off the heat. Ladle into containers immediately so the spinach does not continue cooking in residual heat.