Mixed dish (5)
(Other definitions for casserole that I've seen before include "Slow-cooked dish" , "So cereals may be used for this oven-cooked covered dish" , "Make a stew" , "Oven dish" , "Cook slowly" .)
(Other definitions for stew that I've seen before include "Large watercourse" , "West (anag.)" , "Tight spot" , "State of mental agitation (informal)" , "Cook by long slow simmering" .)
'mixed dish' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for salad that I've seen before include "A cold meal with lots of lettuce" , "Curve" , "one gets dressed" , "rabbit food" , "Food dish" .)