Place the chickpeas in a large bowl, cover with 2 inches of water and soak overnight.
Drain the chickpeas and place them in a large saucepan, cover with water and bring to a boil over high heat. Lower the heat to medium-low and cook until the chickpeas are tender, about 2 hours. Remove from the heat and set the chickpeas aside to cool in the water.
Lay a large piece of plastic wrap on the counter (make sure it is longer than the length of your fish fillet). Mix the rock salt and saffron together in a small bowl, then sprinkle half of it over the plastic wrap. Place the pollock on top and sprinkle the remaining salt mixture over the top of the fish. Wrap the plastic wrap tightly around the fish and refrigerate it for 1 1/2 to 2 hours.
Heat the olive oil in a heavy-bottomed oven-safe pot (such as a Dutch oven) or shallow casserole dish over medium heat. Add the onions, grated garlic and red chiles and cook until the onions are soft, 4 to 6 minutes. Add the chorizo and cook until the red paprika oil renders out of the sausage, about 5 minutes. Stir in the bay leaves, cumin, paprika, and cinnamon stick and cook until the cinnamon is fragrant, 3 to 4 minutes.
Preheat the oven to 325 degrees F. Drain the chickpeas and add them to the chorizo mixture along with the chicken stock and canned tomatoes. Bring to a boil over high heat and then cook in the oven for 45 minutes. Remove the stew from the oven and season to taste with salt and freshly ground black pepper.
Wash the pollock thoroughly under cold running water. Pat dry, then place on top of the chickpeas. Return the pot to the oven and cook until the fish is cooked through and flakes easily, 12 to 15 minutes. Gently lift the fish from the pot and place it on a large serving plate.
Stir the spinach into the stew until it is just wilted. Discard the bay leaves and cinnamon stick. Spoon the stew around the fish and serve.