SETI and a reverse solar gravitational lens
So a solar gravitational lens is a telescope that is aimed directly at the sun in order to observe the light that is bent around the sun. Effectively focusing the light rays into a natural telescope. NASA scientists have proposed missions to actually crate various observation satellites so we can observe these exoplanets but no offer has been offficially greenlit.
But what would this effect look like from the other side. If we were being observed by various gravitational lenses and we just looked at various stars to see an eye staring back at us. Obviously this would be pretty difficult to do due to these telescopes being monumentally smaller than actual planets. But if we assume that an advanced alien species used some other detection method to know some basic characteristics of Earth it would be a potentially habitable planet by their estimates and worth creating a specialized telescope for it.
On our end all we would need to do is look back. With a big enough telescope of course.