Is it a problem to warm on Shabbos raw green-beans that are edible on a hot plate? The green-beans will become soft and hot, and maybe also crispy (They are from a frozen bag, but they have already defrosted)
Yes there is a problem with heating any uncooked food, more than Yad Soledes Bo, (approx. 110oF or 44oC ) as it is considered cooking it, and Meleches Bishul. They may however be put near the hot plate that even if it is kept there for a long time, will only be able to get lukewarm.
S.A. O.C. 318-4, Igros Moshe O.C. 4-74 Bishul-3, Minchas Shlomo 1-91.