Sort of soup on which a chap can get lit up! (6)
I believe the answer is:
lentil
'sort of soup on which' is the definition.
'lentil' can be an answer for 'sort of soup'. I'm not sure about the rest of the definition.
'a chap can get lit up' is the wordplay.
'a chap can' becomes 'len' (I can't justify this - if you can you should give a lot more credence to this answer).
'get' says to put letters next to each other.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'lit' reversed gives 'til'.
'len'+'til'='LENTIL'
Can you help me to learn more?
(Other definitions for lentil that I've seen before include "Small edible seed" , "Plant - pulse" , "Lintel (anag.)" , "Vegetarian food" , "Edible seed of bean plant" .)