Moq: How to get to a parameter passed to a method of a mocked service

Imagine this class

public class Foo {

    private Handler _h;

    public Foo(Handler h)
    {
        _h = h;
    }

    public void Bar(int i)
    {
        _h.AsyncHandle(CalcOn(i));
    }

    private SomeResponse CalcOn(int i)
    {
        ...;
    }
}

Mo(q)cking Handler in a test of Foo, how would I be able to check what Bar() has passed to _h.AsyncHandle?