GestureRecognizer.cs

private void SetupGestureRecognizer()
{
  this.MapView.AddGestureRecognizer(new UITapGestureRecognizer(r => {
    PointF pointInView = r.LocationInView(this.MapView);
    CLLocationCoordinate2D touchCoordinates = this.MapView.ConvertPoint(pointInView, this.MapView);
    MKMapPoint mapPoint = MKMapPoint.FromCoordinate(touchCoordinates);
    
    foreach (NSObject overlay in this.MapView.Overlays)
    {
      if (overlay is MKPolygon)
      {
        MKPolygon polygon = (MKPolygon)overlay;
	MonoTouch.MapKit.MKOverlayView view = this.MapView.ViewForOverlay(polygon);

	if (view is MKPolygonView)
	{
	  MKPolygonView polygonView = (MKPolygonView)view;
	  PointF polygonViewPoint = polygonView.PointForMapPoint(mapPoint);
	  bool isInView = polygonView.Path.ContainsPoint(polygonViewPoint, false);

	  if (isInView)
	  {
	    string message = string.Concat("You tapped ", polygon.Title);
	    UIAlertView alertView = new UIAlertView("Tap recognized!", message, null, "OK");
	    alertView.Show ();
	  }
	}
      }
    }
  }));
}