We report, to the best of our knowledge, the first monolithic erbium-doped fluorozirconate fiber laser bounded by two fiber Bragg gratings (FBGs) operating at 3.55 μm. Its output power and total optical efficiency are 5.6 W and 26.4% respectively, the highest ever achieved at this wavelength from a fiber laser. The monolithic design of the cavity also increases its stability and prevents fiber tip damage which has limited prior demonstrations to a maximum output power of 1.5 W. This Letter also studies the performances of the laser cavity for various output FBG reflectivities and presents numerical modeling results exhibiting remarkable agreement with experimental results.