Small boy full of strange ideas for a dish (4,5)
I believe the answer is:
Here is my best explanation:
'a dish' is the definition.
'small boy full of strange ideas' is the subsidiary indication.
'small' becomes 's' (abbreviation - e.g. clothes size).
'boy' becomes 'lad' (lad is a kind of boy**).
'full of' means one lot of letters goes inside another.
'strange' is an anagram indicator.
'ideas' with letters rearranged gives 'idesa'.
'slad' enclosing 'idesa' is 'sidesalad'.
'for' is the link.
(Another definition for side salad that I've seen is "Extra dish of lettuce, tomato etc?".)