Technological breakthroughs in telescope development have always driven discoveries in astronomy. Discoveries are yet to be made in the energy band between a few hundred keV and a few MeV, which is currently under-explored due to the lack of sufficiently sensitive telescopes. The MeV regime faces significant technology challenges due to the changing nature of the photon-matter interaction in this band. Yet, for many astrophysical high-energy sources the radiative power peaks in the MeV window. To address this issue, the Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) combines a coded-mask telescope and a Compton telescope. The former allows disentangling sources in crowded regions with its high angular resolution of ~1 arcmin and is complemented by the latter due to its high sensitivity to diffuse emission. The ability to separate diffuse emission and point sources allows exploring the acceleration of cosmic rays, the origin of the Fermi Bubbles, the diffuse 511 keV positron annihilation line, sites of explosive element synthesis, and testing for dark matter candidates. Various classes of jetted active galactic nuclei exhibit variable spectra in this under-explored energy range and GECCO observations will advance our understanding of how their central supermassive black holes evolve over cosmic time and how they accelerate particles. The GECCO consortium is currently undergoing mission design and is open to scientists interested in its technology and the many astrophysical frontier questions that remain to be adequately addressed in the MeV window.