Abstract: The chemo-structural evolution of galaxies at the peak epoch of cosmic star formation is a key issue in galaxy evolution physics that we do not yet fully understand. To address this, we investigate the spatial distribution of gas-phase metallicity in emission-line galaxies in the redshift range of z~1-3. For the first time, we bring forward a novel method of obtaining sub-kpc resolution metallicity maps using grism spectroscopy of strongly lensed galaxies. The sufficient spatial sampling, achievable only through the synergy of diffraction-limited data and lensing magnification at high redshift, is crucial to avoid spuriously flat gradient measurements. In our most recent paper (Wang et al. 2017), we publish 10 unbiased metallicity maps, using the deep HST/WFC3 near infrared grism data acquired by the Grism Lens-Amplified Survey from Space (GLASS). Our maps reveal diverse galaxy morphologies, indicative of various effects such as efficient radial mixing from tidal torques, rapid accretion of low-metallicity gas, and other physical processes which can affect the gas and metallicity distributions in individual galaxies. Tying theories to data, we find that predictions given by analytical chemical evolution models assuming a relatively extended star-formation profile in the early disk formation phase can explain the majority of observed metallicity gradients, without involving galactic feedback or radial outflows. We also observe an intriguing correlation between stellar mass and metallicity gradient, consistent with the ``downsizing'' galaxy formation picture that more massive galaxies are more evolved into a later phase of disk growth, where they experience more coherent mass assembly at all radii and thus show shallower metallicity gradients. Our published 10 gradients constitute one third of the entire sample of currently existing sub-kpc resolution metallicity gradient measurements at high redshift. The analysis of the entire GLASS dataset will bring about over 100 more. Our results will revolutionize our understanding of the cycling of metals and how that regulates galaxy growth.