>"If you put one lasgana on topnof another lasagna you still onky have one lasagna...."
That's because it's a mass noun, like money or time. It doesn't take the 's' in most constructions.
(Unlike "onky" which is an Equidae in upper-class Bostonian* dialects and takes the "ies" for plural.)
(* - not to be confused with the other Equidae thoroughbred)