Heat the oil in a large heavy skillet over medium heat.
Sautee onions until starting to brown.
Add chicken pieces, and fry until lightly browned on the outside.
Pour in the water, and bring to a boil. Reduce heat to low, and simmer for about 30 minutes, adding more water if necessary to keep the mixture from drying out.
Preheat the oven to 325 degrees F (65 degrees C).
Combine the walnuts and pomegranate juice in the container of a blender or food processor. Process into liquid. This can be done in small batches if necessary.
Add this mixture to the simmering chicken mixture. Season with cardamom, cinnamon, saffron powder, and salt. Stir in the cubed squash.
Transfer the entire mixture to a 9x13 inch baking dish.
Bake, loosely covered for 2 1/2 hours in the preheated oven.