Today's theme is about a bunch of flowers (7)
I believe the answer is:
dahlias
'bunch of flowers' is the definition.
'dahlias' can be an answer for 'flowers' (dahlia is a kind of flower). I am not sure about the 'bunch of' bit.
'today's theme is about a' is the wordplay.
'today's theme' becomes 'dahl' (I can't explain this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'is' placed around 'a' is 'ias'.
'dahl'+'ias'='DAHLIAS'
Can you help me to learn more?
(Other definitions for dahlias that I've seen before include "Might Ali dash for the flowers?" , "Tuberous garden plants" , "bloomers" , "Flowers for Shia lad" , "I had Al's fowers" .)