Try eating every single species of onion (7)
I believe the answer is:
shallot
'species of onion' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for shallot that I've seen before include "Rowing boat" , "It resembles an onion" , "Type of 12" , "Edible onion-like bulb" , "Small onion-like bulb used for seasoning" .)