Use the existing Event system. Attach a UIEventTrigger script to your button in the inspector. Add your script and method with its one parameter in the OnPress event. You pass an object to the parameter and select a property from it. I use a super simple script that just has a public int attached for things like level selection, and I pass that as a parameter in the UIEventTrigger parameter.
So I have two scripts on a level selection button, UI_Number that just has a public int, and UIEventTrigger that passes this int value to the script.