Enthusiasts of diet sandwiches left thank-you note before tea delivered (10)

'enthusiasts of diet sandwiches' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe there's an association between them I don't understand?

'left thank-you note before tea delivered' is the wordplay.
I cannot really understand how this works, but
'left' could be 'l' (common abbreviation) and 'l' is present in the answer.
'note' could be 'ti' (musical note, as in do re mi so fa la ti do) and 'ti' is found in the answer.
'tea' could be 't' (I've seen this in other clues) and 't' is located in the answer.
'thank you' could be 'ta' (informal way of saying thank you) and 'ta' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?