This is a question across all pantheons and mythologies. Overall what is the easiest way to become a god? It should be an one-time act. But perhaps for simplicity sake we can use immortality as the main attribute of godhood.
So we do not count being born a god; neither being made a god by the other gods, given how fickle they are; nor the continued use of Idun's apples.
EDIT: Alright, so some more information for better understanding. The standard way to become a god is through apotheosis (or currently divinization). This is however only after death. Remember Hercules, Roman Emperors, the Chinese Emperors, various Saints...
What I am looking for is quite similar to Gilgamesh's quest for immortality. He did find a plant that at least restored youth. Or sometimes Ambrosia is described as granting not only immortality, but making a god out of a mortal.
Also in Taoism humans are able to gain immortality and god-like powers.
So I ask again, across the plethora of mythologies that exist in the world, what is the easiest way a mortal can become a god?
I truly have to draw a parallel with Gilgamesh and his search for immortality here. First he visits Utnapishtim, whose type of immortality is ideal, but was a gift from a god, so not easily obtainable. I am unsure if successfully passing Utnapishtim's test would have led to something, but this appears to me as the most easiest way. Then there is the Ur-shanabi, which is probably the same thing as ambrosia, Idun's apples, but we cannot be sure, so it could be an solution. Finally we have the solution of cultural immortality, which is for me not a solution at all, given that he feared to become a forgotten rotting corpse, and become a remembered rotting corpse.
So what if Gilgamesh was more open minded and cunning. Why settle for immortality when you can become a god? Why limit the search in Mesopotamia, when there is the whole world. Within all the world religions what is the easiest way to become a god?