Hello,

in your mosueclicked part
      have a boolean var that gets true when clicked (it could have the name bCircleShow - with b for
      boolean)


in your setup()

1. opacity=255;
2. bCircleShow= false;
   

in your draw()
when bCircleShow is true, have a var diameter for your circle and make this diameter bigger
the fill-color you can make more transparent each time
so it would be something like (not tested)

1. if (bCircleShow) {
2.    fill(255,2,2,opacity);
3.    ellipse (11,11,diameter ,diameter );
4.    diameter ++;
5.    opacity--;
6. }

of course you have to init the vars, make them with global scope

Greetings, Chrisir