Adding a click event to an element?

How can one assign a click event to an arbitrary span (eg. <span id="foo">foo</span>) in an ST2 app?

I have a trivial example that illustrates the idea of what I'd like to do. In the example, I write the letters A,B,C and I'd like to tell the user which letter they clicked.

Here's an image:

CODE SNIPPET

Ext.application({

    launch: function() {
        var view = Ext.create('Ext.Container', {

            layout: {
                type: 'vbox'
            },
            items: [{
                html: '<span id="let_a">A</span>  <span id="let_b">B</span> <span style="float:right" id="let_c">C</span>',
                style: 'background-color: #c9c9c9;font-size: 48px;',
                flex: 1
            }]
        });
        Ext.Viewport.add(view);
    }
});