Semiconductor polariton systems offer a versatile solid state platform to study many-body physical effects such as lasing or superfluidity in out-of-equilibrium systems. They are also anticipated as a new platform for integrated optics: behaving as interacting photons, these mixed light-matter quasi-particles could be the cornerstone of a new technology for optoelectronic devices, implementing logic gates, switches and other functionalities. In this work we demonstrate an electrically controlled polariton laser, in a compact, easy-to-fabricate and integrable configuration, based on a semiconductor waveguide. Interestingly, we show that polariton lasing can be achieved in a system without a local minimum in the polariton energy-momentum dispersion. The surface cavity modes for the laser emission are obtained by adding couples of specifically designed diffraction gratings on top of the planar waveguide, forming an in-plane Fabry-Perot cavity. It is precisely thanks to the waveguide geometry, that we can apply a transverse electric field in order to finely tune the laser energy and quality factor of the cavity modes. Remarkably, we exploit the system sensitivity to the applied electric field to achieve an electrically switched source of coherent polaritons. The precise control that can be reached with the manipulation of the grating properties and of the electric field, provide strong advantages to this device in terms of miniaturization and integrability, two main features for the future development of coherent sources from polaritonic technologies.