The ability to shape light spectra dynamically and arbitrarily would revolutionize many photonic systems by offering unparalleled spectral efficiency and network flexibility. However, most existing optical components have rigid spectral functionalities with limited tunability, hindering compact and fast optical spectral shaping. We introduce a pixelated nano-opto-electro-mechanical (NOEM) grating that exploits electromechanically induced symmetry breaking for precise, pixel-level control of grating coupling strength, yielding a miniaturized (~0.007 mm²) on-chip spectral shaper. We demonstrate the synthesis of grating pixels for arbitrary spectral responses and achieve rapid (<10 ns), high-contrast (>100 dB) wavelength-selective switching via collective, nanometer-scale electrostatic perturbations. Our pixelated NOEM grating delivers exceptional spectral manipulation capabilities in an ultracompact, on-chip manner, offering prospects for next-generation optical information networks, computing architectures, and beyond.