Right click listener - generated canvas buttons

I know how to add an onClick listener to a button that is generated by script, the only problem is that it just detects left mouse button clicks. And I need it to detect left and right mouse button clicks to make an inventory system.

To add a onClick listener:

 slot.GetComponent<Button>().onClick.AddListener(() => { SlotClick(); });

where:

slot is the button

SlotClick is the function

And I would like to know how the AddListener syntax works. Like what means it's parameters:

 () => { SlotClick(); }

Thanks in advance and sorry if my english is bad :)