Jack, say, stuffed with hot leafy greens (5)
I believe the answer is:
chard
'leafy greens' is the definition.
'chard' can be an answer for 'greens' (chard is a kind of greens). I am unsure of the 'leafy' bit.
'jack say stuffed with hot' is the wordplay.
'jack say' becomes 'card' (jack is a type of playing card).
'stuffed with' means one lot of letters goes inside another (some letters get stuffed inside).
'hot' becomes 'h' (abbreviation eg on taps).
'card' going around 'h' is 'CHARD'.
Can you help me to learn more?
(Other definitions for chard that I've seen before include "Beet with edible leaves and stalks" , "Type of beet" , "A beet; sounds like burnt" , "Kind of (Swiss?) beet with edible leaves" , "Vegetable; Somerset town" .)