Big fire in centre of Toronto consuming plant (7)
I believe the answer is:
inferno
'big fire' is the definition.
(I've seen this before)
'in centre of toronto consuming plant' is the wordplay.
'centre of' says to take the centre.
'consuming' means one lot of letters goes inside another.
'plant' becomes 'fern' (fern is a kind of plant**).
The middle letter of 'toronto' is 'o'.
'in'+'o'='ino'
'ino' placed around 'fern' is 'INFERNO'.
(Other definitions for inferno that I've seen before include "(Fiery) Hell" , "Dante's scene of horror" , "Dante's Hell" , "Uncontrollable fire" , "Furious" .)