Cast iron pans shouldn't really be washed - so if yours is new, you will have to *season* it before use so that it stops food sticking.... Just apply a little oil before use. After cooking, rub with a little salt and wipe down with a little oil before storing it away (I place a piece of kitchen paper over the top of my oiled cast iron frying pans and woks to stop dust etc sticking to them). (More info here:-
http://forums.moneysavingexpert.com/showthread .html?p=540497)
I thought the griddle pans were really for cooking *greasy* food, so that the oil/fat ran off into the recesses and not back into the food. For frying rissoles, veggie burgers etc, I'd use a flat based frying pan, not a ridged one. If your griddle pan is not ridged, take no notice of this paragraph !