I´m almost sure that this was answered before, but I couldn´t find the thread.
How to get and call Lua functions from a method defined in tolua?
local button = Button:new("Click me!")
button._onClick_ = button_onClick
button.onClick( button_onClick )
Then, the class Button must call the function when the button is clicked.
How to get a reference for a Lua function in tolua, and how to call it later?