For standard events like the menu loading, we can use a function to register events. Below is a working callback:
local function MenuLoadedEvt(Sender, EventArgs)
-- Do something (Sender = Hud, EventArgs = Arguments for event)
end
-- The event name and callback
Hud:registerEventHandler("menu_loaded", MenuLoadedEvt)
Each element has a specific set of events. In addition, event arguments change per-event.