  In this letter, we exploit the gravitational potential of the rich cluster
A2218 as a magnifying glass. We demonstrate that the magnification due to the
cluster allows us to observe distant background galaxies at a comparable level
of detail to galaxies at z~0.1. Using the GMOS Integral Field Unit on Gemini
North we observed the spatially-resolved [OII](3727) emission line spectrum for
a lensed disk-galaxy at z=1.034. Using a detailed model for the cluster mass
distribution, we are able to correct for the lensing by the cluster and
reconstruct the source morphology. We find that the overall magnification is a
factor of 4.92 +/- 0.15, and the rest-frame absolute I-band magnitude is
M_{I}^{rest} = -22.4 +/- 0.2, where the error bars include conservative
estimates of the uncertainty in the source-plane reconstruction. The
inclination-corrected circular velocity is 206 +/- 18km/s. The galaxy lies very
close to the mean Tully-Fisher relation of present-day spirals. Although our
results are based on a single object, they demonstrate that gravitational
lensing can be viably used to make detailed studies of the evolution of the
structure of distant field galaxies.
