Comparing a range of recipes for chicken and rice casseroles gives a range of between 325 and 400 degrees Fahrenheit for this type of dish. Fan assisted ovens usually require a lower temperature than conventional ovens.
Fan assisted ovens have consistent temperatures throughout, but conventional ovens have hot spots and vary in temperature. The setting chosen needs to take the placement of the casserole dish in the oven into account. Lower temperatures are also better for retaining moisture while higher temperatures encourage a Maillard reaction that enhances flavor and shows as browning. Rice and chicken both require thorough cooking to prevent food poisoning, so sufficient liquid in the casserole to let it cook for around 45 minutes without burning at the chosen temperature is necessary.