Seeds pasted by finalist in Miami wearing trendy cap back-to-front (6)
I believe the answer is:
tahini
'seeds pasted' is the definition.
(paste of sesame seeds)
'finalist in miami wearing trendy cap back-to-front' is the wordplay.
'finalist in' indicates one should take the final letters.
'wearing' is an insertion indicator.
'trendy' becomes 'in' ('in' can mean fashionable).
'cap' becomes 'hat' (cap can mean a hat).
'back-to-front' says the letters should be written in reverse.
The last letter of 'miami' is 'i'.
'in'+'hat'='inhat'
'i' going into 'inhat' is 'inihat'.
'inihat' back-to-front is 'TAHINI'.
'by' is the link.
(Other definitions for tahini that I've seen before include "Sesame seed paste" , "Paste of sesame seeds" , "Sesame-seed based foodstuff" , "Sesame paste; in a hit (anag.)" .)