We demonstrate experimentally a metasurface built from Ag and Al meta-atoms, which exhibits a very peculiar nonlinear response: upon illumination from one side, it produces a very strong second harmonic response, while this is not at all the case for illumination from the other side. I will discuss the underlying mechanisms that lead to this effect, especially the role of bi-anisotropy both at the fundamental and second harmonic frequencies. The linear and non-linear susceptibilities of the system can be retrieved from numerical simulations. I will also discuss whether this device is reciprocal or not.