Mexican green vs ganja

Mexican green and ganja both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mexican green	Yes	No	No	No
ganja	Yes	No	No	No

As nouns, ganja is a hypernym of Mexican green; that is, ganja is a word with a broader meaning than Mexican green:

Mexican green: a particularly potent variety of marijuana
ganja: the most commonly used illicit drug; considered a soft drug, it consists of the dried leaves of the hemp plant; smoked or chewed for euphoric effect

Other hypernyms of Mexican green include cannabis, marihuana, marijuana.

Mexican green (noun)	ganja (noun)
a particularly potent variety of marijuana	the most commonly used illicit drug; considered a soft drug, it consists of the dried leaves of the hemp plant; smoked or chewed for euphoric effect
	a strong-smelling plant whose dried leaves can be smoked for a pleasant effect or pain reduction