A. Onion rings generally consist of a cross-sectional "ring" of onion dipped in batter or bread crumbs and then deep fried.
Vessen Brocho and the Laws of Brochos (p. 375) rule that when fried with a flour coating the brocho is Mezonos.
Horav Shlomo Miller's Shlit'a opinion is that it depends on the thickness of the batter of flour that for considering it Mezonos has to be significant.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a.