  We present a measurement of the mass-metallicity relation (MZR) at cosmic
noon, using the JWST near-infrared wide-field slitless spectroscopy obtained by
the GLASS-JWST Early Release Science program. By combining the power of JWST
and the lensing magnification by the foreground cluster A2744, we extend the
measurements of the MZR to the dwarf mass regime at high redshifts. A sample of
50 galaxies with several emission lines is identified across two wide redshift
ranges of $z=1.8-2.3$ and $2.6-3.4$ in the stellar mass range of
$\log{(M_*/M_\odot)}\in [6.9, 10.0]$. The observed slope of MZR is $0.223 \pm
0.017$ and $0.294 \pm 0.010$ at these two redshift ranges, respectively,
consistent with the slopes measured in field galaxies with higher masses. In
addition, we assess the impact of the morphological broadening on emission line
measurement by comparing two methods of using 2D forward modeling and line
profile fitting to 1D extracted spectra. We show that ignoring the
morphological broadening effect when deriving line fluxes from grism spectra
results in a systematic reduction of flux by $\sim30\%$ on average. This
discrepancy appears to affect all the lines and thus does not lead to
significant changes in flux ratio and metallicity measurements. This assessment
of the morphological broadening effect using JWST data presents, for the first
time, an important guideline for future work deriving galaxy line fluxes from
wide-field slitless spectroscopy, such as Euclid, Roman, and the Chinese Space
Station Telescope.
