Set on fire with dieting? (7)

I believe the answer is:

ignited

I'm a little stuck... Click here to teach me more about this clue!

'set on fire' is the definition.
(I've seen this before)

'dieting?' is the wordplay.
'dieting' anagrams to 'IGNITED'.
However, I'm unsure how this is indicated.

'with' is the link.

Can you help me to learn more?

(Other definitions for ignited that I've seen before include "Sparked off" , "Kindled" , "Set on fire" , "Set alight" , "Gin diet (anag.)" .)

I've seen this clue in The Irish Independent.

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