We present a minimally invasive endomicroscope that performs frequency-domain fluorescence lifetime imaging (FD-FLIM) through a single multimode fiber (MMF), enabling quantitative metabolic contrast at microscopic resolution. The system, termed FLIMME, uses amplitude-modulated 405 nm excitation and lock-in detection to map endogenous fluorophores (NADH, FAD) with temporal accuracy of ±0.03 ns and lifetime resolution down to 0.5 ns. Validation with reference dyes shows excellent agreement with a commercial time-domain FLIM microscope. Ex vivo murine submandibular gland imaging demonstrates label-free visualization of tissue microstructure and metabolic heterogeneity. FLIMME bridges advanced photonics and translational oncology. Its ultrathin, needle-like design allows insertion into surgical sites for potential real-time metabolic imaging of tumor margins.