Protein bean (4)
I believe the answer is:
soya
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">protein bean</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for soya that I've seen before include "Bean used to make tofu" , "Protein-rich bean" , "I'm rich in oil" , "Asian bean yielding edible oil and flour" , "Type of bean" .)