  We present near-infrared observations of 42 gravitationally lensed galaxies
obtained in the framework of the KMOS Lensed Emission Lines and VElocity Review
(KLEVER) Survey, a program aimed at investigating the spatially resolved
properties of the ionised gas in 1.2<z<2.5 galaxies by means of a full coverage
of the YJ, H and K near-infrared bands. Detailed metallicity maps and gradients
are derived for a sub-sample of 28 galaxies from reconstructed source plane
emission line maps, exploiting the variety of different emission line
diagnostics provided by the broad wavelength coverage of the survey. About 85%
of these galaxies are characterised by metallicity gradients shallower than
0.05 dex/kpc and 89% are consistent with flat slope within 3$\sigma$ (67%
within 1$\sigma$), suggesting a mild evolution with cosmic time. In the context
of cosmological simulations and chemical evolution models, the presence of
efficient feedback mechanisms and/or extended star formation profiles on top of
the classical "inside-out" scenario of mass assembly is generally required to
reproduce the observed flatness of the metallicity gradients beyond z$\sim$1 .
Three galaxies with significantly (> 3$\sigma$) "inverted" gradients are also
found, showing an anti-correlation between metallicity and star formation rate
density on local scales, possibly suggesting recent episodes of pristine gas
accretion or strong radial flows in place. Nevertheless, the individual
metallicity maps are characterised by a variety of different morphologies, with
flat radial gradients sometimes hiding non-axisymmetric variations on kpc
scales which are washed out by azimuthal averages, especially in interacting
systems or in those undergoing local episodes of recent star formation.
