Thoughtfully, in a manner of speaking, he'd get stuffed turkey from The Foundation (9)

'thoughtfully' is the definition.
Both the definition and answer are adverbs. Perhaps they are linked in a way I don't understand?

'a manner of speaking he'd get stuffed turkey from the foundation' is the wordplay.
I cannot quite understand how this works, but
'stuffed' could be 'full' ('full' can be similar in meaning to 'stuffed') and 'full' is found in the answer.
The remaining letters 'heedy' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'in' acts as a link.

Can you help me to learn more?